Condensed Consolidated Statements of Operations - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Income Statement [Abstract]
Revenue	$ 383,929	$ 365,944	$ 1,171,304	$ 1,086,849
Cost of services	292,457	280,560	879,673	818,997
Gross profit	91,472	85,384	291,631	267,852
Selling, general and administrative expenses	39,616	36,419	120,403	110,154
Amortization of intangible assets	7,141	7,224	21,338	20,978
Income from operations	44,715	41,741	149,890	136,720
Interest income	20	32	64	117
Interest expense	(10,522)	(10,362)	(31,554)	(30,831)
Income before income taxes	34,213	31,411	118,400	106,006
Income tax expense	(11,703)	(10,853)	(40,760)	(35,997)
Net income	$ 22,510	$ 20,558	$ 77,640	$ 70,009
Earnings per common share:
Common stock-basic (usd per share)	$ 0.38	$ 0.34	$ 1.30	$ 1.14
Common stock-diluted (usd per share)	$ 0.37	$ 0.33	$ 1.27	$ 1.11
Weighted average number of common shares outstanding:
Common stock-diluted (shares)	60,275,902	61,846,725	60,737,185	62,631,444