Segment Information Segment Information - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	$ 205,304	$ 219,289	$ 645,780	$ 644,488
Healthcare
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	87,406	100,000	268,340	295,621
Business Advisory
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	66,048	62,519	201,423	183,602
Education [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	51,850	56,770	176,017	165,265
Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	204,124	216,997	642,951	637,218
Transferred over Time [Member] | Healthcare
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	86,413	98,204	265,813	289,452
Transferred over Time [Member] | Business Advisory
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	66,048	62,519	201,423	183,602
Transferred over Time [Member] | Education [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	51,663	56,274	175,715	164,164
Transferred at Point in Time [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	1,180	2,292	2,829	7,270
Transferred at Point in Time [Member] | Healthcare
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	993	1,796	2,527	6,169
Transferred at Point in Time [Member] | Business Advisory
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	0	0	0	0
Transferred at Point in Time [Member] | Education [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	187	496	302	1,101
Full-time Billable Consultants [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	171,658	181,201	531,173	528,125
Full-time Billable Consultants [Member] | Healthcare
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	65,084	72,142	188,750	206,508
Full-time Billable Consultants [Member] | Business Advisory
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	62,340	60,131	191,566	177,279
Full-time Billable Consultants [Member] | Education [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	44,234	48,928	150,857	144,338
Full-time Equivalents [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	33,646	38,088	114,607	116,363
Full-time Equivalents [Member] | Healthcare
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	22,322	27,858	79,590	89,113
Full-time Equivalents [Member] | Business Advisory
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	3,708	2,388	9,857	6,323
Full-time Equivalents [Member] | Education [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	7,616	7,842	25,160	20,927
Fixed-price Contract [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	83,124	102,361	267,051	299,494
Fixed-price Contract [Member] | Healthcare
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	51,491	65,610	158,079	188,875
Fixed-price Contract [Member] | Business Advisory
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	20,675	24,333	73,442	72,693
Fixed-price Contract [Member] | Education [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	10,958	12,418	35,530	37,926
Time-and-materials Contract [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	90,352	87,207	285,246	257,792
Time-and-materials Contract [Member] | Healthcare
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	14,627	12,307	43,389	39,345
Time-and-materials Contract [Member] | Business Advisory
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	40,511	35,212	118,364	104,325
Time-and-materials Contract [Member] | Education [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	35,214	39,688	123,493	114,122
Performance-based [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	19,312	17,927	55,640	52,954
Performance-based [Member] | Healthcare
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	15,641	16,313	49,042	50,144
Performance-based [Member] | Business Advisory
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	3,671	1,614	5,903	2,810
Performance-based [Member] | Education [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	0	0	695	0
Software Service, Support and Maintenance Arrangement [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	12,516	11,794	37,843	34,248
Software Service, Support and Maintenance Arrangement [Member] | Healthcare
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	5,647	5,770	17,830	17,257
Software Service, Support and Maintenance Arrangement [Member] | Business Advisory
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	1,191	1,360	3,714	3,774
Software Service, Support and Maintenance Arrangement [Member] | Education [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	$ 5,678	$ 4,664	$ 16,299	$ 13,217