Reportable Segments - Operations of Segments (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Segment Reporting Information [Line Items]
Net service revenues	$ 327,699	$ 341,575	$ 337,353	$ 312,611	$ 318,739	$ 313,810	$ 302,758	$ 282,024	$ 1,319,238	$ 1,217,331	$ 1,073,728
Gross profit	$ 103,515	$ 109,821	$ 106,038	$ 94,740	$ 98,378	$ 98,291	$ 94,386	$ 83,526	414,114	374,581	344,376
Operating expenses									342,442	326,624	333,447
Income from continuing operations, before income taxes									71,672	47,957	10,929
Flexible billings
Segment Reporting Information [Line Items]
Net service revenues									1,265,167	1,170,636	1,025,286
Direct Hire fees
Segment Reporting Information [Line Items]
Net service revenues									54,071	46,695	48,442
Operating Segments | Tech
Segment Reporting Information [Line Items]
Net service revenues									895,942	842,469	739,362
Gross profit									261,721	243,085	219,360
Operating Segments | Tech | Flexible billings
Segment Reporting Information [Line Items]
Net service revenues									873,609	823,311	720,179
Operating Segments | Tech | Direct Hire fees
Segment Reporting Information [Line Items]
Net service revenues									22,333	19,158	19,183
Operating Segments | FA
Segment Reporting Information [Line Items]
Net service revenues									325,924	276,811	242,417
Gross profit									119,036	101,071	93,663
Operating Segments | FA | Flexible billings
Segment Reporting Information [Line Items]
Net service revenues									294,186	249,274	213,158
Operating Segments | FA | Direct Hire fees
Segment Reporting Information [Line Items]
Net service revenues									31,738	27,537	29,259
Operating Segments | GS
Segment Reporting Information [Line Items]
Net service revenues									97,372	98,051	91,949
Gross profit									33,357	30,425	31,353
Operating Segments | GS | Flexible billings
Segment Reporting Information [Line Items]
Net service revenues									97,372	98,051	91,949
Operating Segments | GS | Direct Hire fees
Segment Reporting Information [Line Items]
Net service revenues									$ 0	$ 0	$ 0