| 
           PSI acquisition (Details) (USD $) 
         | 
        6 Months Ended | ||||
|---|---|---|---|---|---|
| 
           Mar. 31, 2013
 
          segment 
         | 
        
           Mar. 31, 2013
 
          Policy Studies, Inc 
         | 
        
           Apr. 30, 2012
 
          Policy Studies, Inc 
         | 
        
           Sep. 30, 2012
 
          Policy Studies, Inc
 
          Previously reported 
         | 
        
           Mar. 31, 2013
 
          Policy Studies, Inc
 
          Adjusted 
         | 
      |
| Acquisition Disclosures | |||||
| Share capital acquired (as a percent) | 100.00% | ||||
| Purchase price allocation | |||||
| Accounts receivable and unbilled receivables | $ 23,017,000 | $ 23,017,000 | |||
| Other current assets | 9,527,000 | 9,527,000 | |||
| Deferred income taxes | 2,129,000 | 1,931,000 | 198,000 | ||
| Property and equipment | 6,411,000 | 6,411,000 | |||
| Other assets | 1,332,000 | 1,332,000 | |||
| Intangible assets | 22,183,000 | 22,183,000 | |||
| Total identifiable assets acquired | 64,599,000 | 64,401,000 | 198,000 | ||
| Accounts payable and other liabilities | 20,666,000 | 20,666,000 | |||
| Deferred revenue | 19,775,000 | 19,696,000 | 79,000 | ||
| Total liabilities assumed | 40,441,000 | 40,362,000 | 79,000 | ||
| Net identifiable assets acquired | 24,158,000 | 24,039,000 | 119,000 | ||
| Goodwill | 39,290,000 | 39,161,000 | 129,000 | ||
| Net assets acquired | 63,448,000 | 63,200,000 | 248,000 | ||
| Number of business segments | 2 | ||||
| Net operating loss carryforward included in the purchase price allocation of deferred taxes | $ 10,500,000 | 
| X | ||||||||||
| 
             
- Definition 
          The amount of acquisition cost of a business combination allocated to accounts payable and other liabilities of the acquired entity. No definition available. 
  | 
        
| X | ||||||||||
| 
             
- Definition 
          The amount of acquisition cost of a business combination allocated to other current assets. Does not include amounts allocated to cash and cash equivalents, marketable securities, receivables, inventory, and assets not to be used. No definition available. 
  | 
        
| X | ||||||||||
| 
             
- Definition 
          The net amount recognized as of the acquisition date for the aggregate assets, excluding goodwill, in excess of or less than the aggregate liabilities assumed. No definition available. 
  | 
        
| X | ||||||||||
| 
             
- Details 
          
  | 
        
| X | ||||||||||
| 
             
- Details 
          
  | 
        
| X | ||||||||||
| 
             
- Definition 
          Percentage of voting equity interests acquired in the business combination. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
  | 
        
| X | ||||||||||
| 
             
- Definition 
          The amount of acquisition cost of a business combination allocated to an identifiable intangible asset that will be amortized. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
  | 
        
| X | ||||||||||
| 
             
- Definition 
          The amount of acquisition cost of a business combination allocated to assets acquired. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
  | 
        
| X | ||||||||||
| 
             
- Definition 
          The amount of acquisition cost of a business combination allocated to receivables. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
  | 
        
| X | ||||||||||
| 
             
- Definition 
          The amount of acquisition cost of a business combination allocated to deferred revenue of the acquired entity. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
  | 
        
| X | ||||||||||
| 
             
- Definition 
          Gross amount of acquisition cost of a business combination allocated to noncurrent deferred tax assets. No definition available. 
  | 
        
| X | ||||||||||
| 
             
- Definition 
          Amount of goodwill arising from a business combination, which is the excess of the cost of the acquired entity over the amounts assigned to assets acquired and liabilities assumed. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
  | 
        
| X | ||||||||||
| 
             
- Definition 
          The amount of acquisition cost of a business combination allocated to liabilities assumed. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
  | 
        
| X | ||||||||||
| 
             
- Definition 
          Amount of acquisition cost of a business combination allocated to other noncurrent assets not separately disclosed. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
  | 
        
| X | ||||||||||
| 
             
- Definition 
          The amount of acquisition cost of a business combination allocated to property, plant and equipment to be used in ongoing operations. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
  | 
        
| X | ||||||||||
| 
             
- Definition 
          Net amount recognized for aggregate assets, including goodwill, in excess of or less than the aggregate liabilities assumed (also referred to as net assets acquired). This amount may also be viewed as incremental amount of equity that the consolidated entity (including the portion attributable to a noncontrolling interest) will recognize as a result of the business combination. No definition available. 
  | 
        
| X | ||||||||||
| 
             
- Definition 
          Number of segments reported by the entity. A reportable segment is a component of an entity for which there is an accounting requirement to report separate financial information on that component in the entity's financial statements. No definition available. 
  | 
        
| X | ||||||||||
| 
             
- Definition 
          The sum of domestic, foreign and state and local operating loss carryforwards, before tax effects, available to reduce future taxable income under enacted tax laws. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
  |