Reportable Segments - Operations of Segments (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Segment Reporting Information [Line Items]
Net service revenues	$ 325,998	$ 336,460	$ 335,047	$ 322,201	$ 327,699	$ 341,575	$ 337,353	$ 312,611	$ 1,319,706	$ 1,319,238	$ 1,217,331
Gross profit	$ 99,648	$ 105,380	$ 106,282	$ 97,189	$ 103,515	$ 109,821	$ 106,038	$ 94,740	408,499	414,114	374,581
Operating expenses									352,544	342,442	326,624
Income from continuing operations, before income taxes									55,955	71,672	47,957
Flexible billings
Segment Reporting Information [Line Items]
Net service revenues									1,269,307	1,265,167	1,170,636
Direct Hire fees
Segment Reporting Information [Line Items]
Net service revenues									50,399	54,071	46,695
Operating Segments | Tech
Segment Reporting Information [Line Items]
Net service revenues									883,477	895,942	842,469
Gross profit									255,842	261,721	243,085
Operating Segments | Tech | Flexible billings
Segment Reporting Information [Line Items]
Net service revenues									863,434	873,609	823,311
Operating Segments | Tech | Direct Hire fees
Segment Reporting Information [Line Items]
Net service revenues									20,043	22,333	19,158
Operating Segments | FA
Segment Reporting Information [Line Items]
Net service revenues									337,601	325,924	276,811
Gross profit									120,551	119,036	101,071
Operating Segments | FA | Flexible billings
Segment Reporting Information [Line Items]
Net service revenues									307,245	294,186	249,274
Operating Segments | FA | Direct Hire fees
Segment Reporting Information [Line Items]
Net service revenues									30,356	31,738	27,537
Operating Segments | GS
Segment Reporting Information [Line Items]
Net service revenues									98,628	97,372	98,051
Gross profit									32,106	33,357	30,425
Operating Segments | GS | Flexible billings
Segment Reporting Information [Line Items]
Net service revenues									98,628	97,372	98,051
Operating Segments | GS | Direct Hire fees
Segment Reporting Information [Line Items]
Net service revenues									$ 0	$ 0	$ 0