| Earnings Per Share | 3 Months Ended | |||||||||||||||||||||||||||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Dec. 31, 2017 | ||||||||||||||||||||||||||||||||||||||||||||||||||
| Earnings Per Share [Abstract] | ||||||||||||||||||||||||||||||||||||||||||||||||||
| Earnings Per Share | Earnings Per Share The weighted average number of shares outstanding used to compute earnings per share was as follows: 
 All of our unvested restricted stock units (RSUs) are included in the calculations of dilution above. | |||||||||||||||||||||||||||||||||||||||||||||||||