Consolidated Statements of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Cumulative-effect adjustment	Cumulative Effect, Period of Adoption, Adjusted Balance	Common Stock	Common Stock Cumulative Effect, Period of Adoption, Adjusted Balance	Treasury Stock	Treasury Stock Cumulative Effect, Period of Adoption, Adjusted Balance	Additional Paid-In Capital	Additional Paid-In Capital Cumulative Effect, Period of Adoption, Adjusted Balance	Retained Earnings	Retained Earnings Cumulative-effect adjustment	Retained Earnings Cumulative Effect, Period of Adoption, Adjusted Balance	Accumulated Other Comprehensive Loss	Accumulated Other Comprehensive Loss Cumulative-effect adjustment	Accumulated Other Comprehensive Loss Cumulative Effect, Period of Adoption, Adjusted Balance
Beginning balance (in shares) at Dec. 31, 2017				130,075	130,075	75,484	75,484
Beginning balance at Dec. 31, 2017	$ 530,879	$ 2,091	$ 532,970	$ 1,301	$ 1,301	$ (491,046)	$ (491,046)	$ 675,504	$ 675,504	$ 345,302	$ 2,091	$ 347,393	$ (182)		$ (182)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	61,570									61,570
Other comprehensive income (loss)	(300)												(300)
Share repurchases (in shares)						848
Share repurchases	(17,484)					$ (17,484)
Restricted stock (in shares)				272
Restricted stock	0			$ 3				(3)
Stock options exercised (in shares)				864
Stock options exercised	6,291			$ 8				6,283
Share-based compensation	6,866							6,866
Business acquisitions (in shares)				193
Business acquisitions	3,750			$ 2				3,748
Ending balance (in shares) at Dec. 31, 2018				131,404		76,332
Ending balance at Dec. 31, 2018	593,663	$ 0		$ 1,314		$ (508,530)		692,398		408,963	$ (101)		(482)	$ 101
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	70,714									70,714
Other comprehensive income (loss)	(299)												(299)
Share repurchases (in shares)						1,305
Share repurchases	(27,163)					$ (27,163)
Restricted stock (in shares)				228
Restricted stock	0			$ 2				(2)
Stock options exercised (in shares)				1,210
Stock options exercised	10,608			$ 12				10,596
Share-based compensation	7,254							7,254
Business acquisitions (in shares)				214
Business acquisitions	4,461			$ 3				4,458
Ending balance (in shares) at Dec. 31, 2019				133,056		77,637
Ending balance at Dec. 31, 2019	659,238			$ 1,331		$ (535,693)		714,704		479,576			(680)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	78,299									78,299
Other comprehensive income (loss)	(1,589)												(1,589)
Share repurchases (in shares)						2,408
Share repurchases	$ (59,604)					$ (59,604)
Restricted stock (in shares)				25
Stock options exercised (in shares)	634			634
Stock options exercised	$ 6,486			$ 6				6,480
Share-based compensation	8,869							8,869
Business acquisitions (in shares)				429
Business acquisitions	10,921			$ 4				10,917
Ending balance (in shares) at Dec. 31, 2020				134,144		80,045
Ending balance at Dec. 31, 2020	$ 702,620			$ 1,341		$ (595,297)		$ 740,970		$ 557,875			$ (2,269)