Condensed Consolidated Statements of Stockholders' Equity (Unaudited) - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Treasury Stock	Additional Paid-In Capital	Retained Earnings	Accumulated Other Comprehensive Loss
Beginning balance (in shares) at Dec. 31, 2019		133,056	77,637
Beginning 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	58,316				58,316
Other comprehensive income (loss)	(1,629)					(1,629)
Share repurchases (in shares)			1,147
Share repurchases	(29,029)		$ (29,029)
Indirect repurchase of shares for minimum tax withholding (in shares)			97
Indirect repurchase of shares for minimum tax withholding	(2,040)		$ (2,040)
Restricted stock units and awards (in shares)		40
Stock options exercised (in shares)		327
Stock options exercised	3,227	$ 3		3,224
Stock-based compensation	4,280			4,280
Business acquisitions (in shares)		113
Business acquisitions	2,857	$ 1		2,856
Ending balance (in shares) at Jun. 30, 2020		133,536	78,881
Ending balance at Jun. 30, 2020	695,220	$ 1,335	$ (566,762)	725,064	537,892	(2,309)
Beginning balance (in shares) at Mar. 31, 2020		133,241	78,811
Beginning balance at Mar. 31, 2020	670,260	$ 1,332	$ (565,180)	719,616	516,424	(1,932)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	21,468				21,468
Other comprehensive income (loss)	(377)					(377)
Indirect repurchase of shares for minimum tax withholding (in shares)			70
Indirect repurchase of shares for minimum tax withholding	(1,582)		$ (1,582)
Restricted stock units and awards (in shares)		40
Stock options exercised (in shares)		211
Stock options exercised	2,214	$ 2		2,212
Stock-based compensation	2,257			2,257
Business acquisitions (in shares)		44
Business acquisitions	980	$ 1		979
Ending balance (in shares) at Jun. 30, 2020		133,536	78,881
Ending balance at Jun. 30, 2020	695,220	$ 1,335	$ (566,762)	725,064	537,892	(2,309)
Beginning balance (in shares) at Dec. 31, 2020		134,144	80,045
Beginning balance at Dec. 31, 2020	702,620	$ 1,341	$ (595,297)	740,970	557,875	(2,269)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	58,816				58,816
Other comprehensive income (loss)	912					912
Share repurchases (in shares)			2,036
Share repurchases	(63,438)		$ (63,438)
Indirect repurchase of shares for minimum tax withholding (in shares)			92
Indirect repurchase of shares for minimum tax withholding	(3,037)		$ (3,037)
Restricted stock units and awards (in shares)		80
Restricted stock units and awards	$ 0	$ 1		(1)
Stock options exercised (in shares)	493	493
Stock options exercised	$ 5,448	$ 5		5,443
Stock-based compensation	5,454			5,454
Business acquisitions (in shares)		175
Business acquisitions	5,557	$ 2		5,555
Ending balance (in shares) at Jun. 30, 2021		134,892	82,173
Ending balance at Jun. 30, 2021	712,332	$ 1,349	$ (661,772)	757,421	616,691	(1,357)
Beginning balance (in shares) at Mar. 31, 2021		134,625	81,209
Beginning balance at Mar. 31, 2021	727,783	$ 1,346	$ (629,439)	749,207	608,084	(1,415)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	8,607				8,607
Other comprehensive income (loss)	58					58
Share repurchases (in shares)			919
Share repurchases	(30,759)		$ (30,759)
Indirect repurchase of shares for minimum tax withholding (in shares)			45
Indirect repurchase of shares for minimum tax withholding	(1,574)		$ (1,574)
Restricted stock units and awards (in shares)		34
Stock options exercised (in shares)		96
Stock options exercised	1,040	$ 1		1,039
Stock-based compensation	2,599			2,599
Business acquisitions (in shares)		137
Business acquisitions	4,578	$ 2		4,576
Ending balance (in shares) at Jun. 30, 2021		134,892	82,173
Ending balance at Jun. 30, 2021	$ 712,332	$ 1,349	$ (661,772)	$ 757,421	$ 616,691	$ (1,357)