Business segments - Schedule of Segment Reporting Results By Segment (Details) $ in Thousands |
3 Months Ended | 12 Months Ended | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
|
Sep. 30, 2019
USD ($)
|
Jun. 30, 2019
USD ($)
|
Mar. 31, 2019
USD ($)
|
Dec. 31, 2018
USD ($)
|
Sep. 30, 2018
USD ($)
|
Jun. 30, 2018
USD ($)
|
Mar. 31, 2018
USD ($)
|
Dec. 31, 2017
USD ($)
|
Sep. 30, 2019
USD ($)
segment
|
Sep. 30, 2018
USD ($)
|
Sep. 30, 2017
USD ($)
|
|
| Segment Reporting [Abstract] | |||||||||||
| Number of business segments | segment | 3 | ||||||||||
| Financial information for each of the Company's business segments | |||||||||||
| Revenue | $ 754,966 | $ 730,710 | $ 736,520 | $ 664,619 | $ 558,446 | $ 597,855 | $ 612,787 | $ 623,148 | $ 2,886,815 | $ 2,392,236 | $ 2,450,961 |
| Gross profit | 168,250 | 174,247 | 169,422 | 159,265 | 138,938 | 154,684 | 148,803 | 151,960 | 671,184 | 594,385 | 611,905 |
| Selling, general and administrative expense | 321,023 | 285,241 | 284,593 | ||||||||
| Operating income | 77,576 | 83,594 | 81,801 | 74,136 | 61,908 | 82,571 | 71,321 | 79,683 | 317,107 | 295,483 | 313,512 |
| Amortization of intangible assets | (33,054) | (10,308) | (12,208) | ||||||||
| Gain on sale of a business | $ 0 | $ 0 | $ 650 | ||||||||
| Percentage of total revenue | 11.00% | 12.40% | 12.80% | ||||||||
| Depreciation and amortization | $ 52,404 | $ 51,884 | $ 55,769 | ||||||||
| Other | |||||||||||
| Financial information for each of the Company's business segments | |||||||||||
| Selling, general and administrative expense | 475 | 503 | (394) | (599) | 865 | 1,032 | 0 | 0 | 2,676 | 2,844 | 1,492 |
| Other | 15 | (1,897) | (1,409) | ||||||||
| Segment Reconciling Items | |||||||||||
| Financial information for each of the Company's business segments | |||||||||||
| Amortization of intangible assets | (9,028) | (9,049) | (9,519) | (5,458) | (2,462) | (2,525) | (2,603) | (2,718) | (33,054) | (10,308) | (12,208) |
| Restructuring costs | 0 | (3,353) | (2,242) | ||||||||
| Acquisition-related expenses | 0 | 0 | 0 | (2,691) | (947) | 0 | 0 | 0 | (2,691) | (947) | (83) |
| Gain on sale of a business | 0 | 0 | 650 | ||||||||
| U.S. Health and Human Services | |||||||||||
| Financial information for each of the Company's business segments | |||||||||||
| Revenue | 1,176,488 | ||||||||||
| U.S. Health and Human Services | Operating segments | |||||||||||
| Financial information for each of the Company's business segments | |||||||||||
| Revenue | 300,406 | 291,132 | 290,737 | 294,213 | 288,944 | 314,477 | 306,249 | 304,241 | 1,176,488 | 1,213,911 | 1,220,086 |
| Gross profit | 83,154 | 86,664 | 86,260 | 88,031 | 87,382 | 101,425 | 86,586 | 84,231 | 344,109 | 359,624 | 348,906 |
| Selling, general and administrative expense | 123,275 | 140,990 | 144,014 | ||||||||
| Operating income | 53,832 | 54,250 | 56,860 | 55,892 | 52,195 | 67,043 | 49,970 | 49,426 | $ 220,834 | $ 218,634 | $ 204,892 |
| Percentage of total revenue | 18.80% | 18.00% | 16.80% | ||||||||
| Depreciation and amortization | $ 18,466 | $ 20,963 | $ 23,374 | ||||||||
| U.S. Federal Services | |||||||||||
| Financial information for each of the Company's business segments | |||||||||||
| Revenue | 1,111,197 | ||||||||||
| U.S. Federal Services | Operating segments | |||||||||||
| Financial information for each of the Company's business segments | |||||||||||
| Revenue | 312,179 | 292,295 | 289,736 | 216,987 | 117,375 | 112,226 | 116,327 | 132,983 | 1,111,197 | 478,911 | 545,573 |
| Gross profit | 66,586 | 66,803 | 60,696 | 47,985 | 33,690 | 32,276 | 27,374 | 33,358 | 242,070 | 126,698 | 139,321 |
| Selling, general and administrative expense | 126,128 | 69,312 | 74,345 | ||||||||
| Operating income | 31,090 | 33,907 | 29,592 | 21,353 | 15,965 | 14,877 | 9,834 | 16,710 | $ 115,942 | $ 57,386 | $ 64,976 |
| Percentage of total revenue | 10.40% | 12.00% | 11.90% | ||||||||
| Depreciation and amortization | $ 16,802 | $ 8,478 | $ 11,175 | ||||||||
| Outside the U.S. | |||||||||||
| Financial information for each of the Company's business segments | |||||||||||
| Revenue | 599,130 | ||||||||||
| Outside the U.S. | Operating segments | |||||||||||
| Financial information for each of the Company's business segments | |||||||||||
| Revenue | 142,381 | 147,283 | 156,047 | 153,419 | 152,127 | 171,152 | 190,211 | 185,924 | 599,130 | 699,414 | 685,302 |
| Gross profit | 18,510 | 20,780 | 22,466 | 23,249 | 17,866 | 20,983 | 34,843 | 34,371 | 85,005 | 108,063 | 123,678 |
| Selling, general and administrative expense | 68,944 | 72,095 | 64,742 | ||||||||
| Operating income | $ 2,157 | $ 4,989 | $ 4,474 | $ 4,441 | $ (945) | $ 4,208 | $ 16,440 | $ 16,265 | $ 16,061 | $ 35,968 | $ 58,936 |
| Percentage of total revenue | 2.70% | 5.10% | 8.60% | ||||||||
| Depreciation and amortization | $ 17,136 | $ 22,443 | $ 21,220 | ||||||||