Consolidated Statements of Stockholders' Equity (Unaudited) - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock [Member]	Treasury Stock [Member]	Additional Paid-In Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive (Loss) Gain [Member]
Balance, Amount at Dec. 31, 2018	$ 593,663	$ 1,314	$ (508,530)	$ 692,398	$ 408,963	$ (482)
Balance, Shares at Dec. 31, 2018		131,404	76,332
Cumulative-effect of accounting changes adjustment					(101)	101
Net income	54,061				54,061
Other comprehensive loss	(341)					(341)
Share repurchases	(21,732)		$ (21,732)
Share repurchases, Shares			1,096
Restricted stock		$ 2		(2)
Restricted stock, Shares		228
Stock options exercised	3,043	$ 4		3,039
Stock options exercised, Shares		378
Stock-based compensation	3,399			3,399
Business acquisitions	1,967	$ 1		1,966
Business acquisitions, Shares		98
Balance, Amount at Jun. 30, 2019	634,060	$ 1,321	$ (530,262)	700,800	462,923	(722)
Balance, Shares at Jun. 30, 2019		132,108	77,428
Balance, Amount at Mar. 31, 2019	623,487	$ 1,318	$ (520,088)	696,226	446,331	(300)
Balance, Shares at Mar. 31, 2019		131,813	76,912
Net income	16,592				16,592
Other comprehensive loss	(422)					(422)
Share repurchases	(10,174)		$ (10,174)
Share repurchases, Shares			516
Restricted stock		$ 1		(1)
Restricted stock, Shares		55
Stock options exercised	1,643	$ 2		1,641
Stock options exercised, Shares		189
Stock-based compensation	1,917			1,917
Business acquisitions	1,017			1,017
Business acquisitions, Shares		51
Balance, Amount at Jun. 30, 2019	634,060	$ 1,321	$ (530,262)	700,800	462,923	(722)
Balance, Shares at Jun. 30, 2019		132,108	77,428
Balance, Amount at Dec. 31, 2019	659,238	$ 1,331	$ (535,693)	714,704	479,576	(680)
Balance, Shares at Dec. 31, 2019		133,056	77,637
Net income	58,316				58,316
Other comprehensive loss	(1,629)					(1,629)
Share repurchases	(31,069)		$ (31,069)
Share repurchases, Shares			1,244
Restricted stock, Shares		40
Stock options exercised	$ 3,227	$ 3		3,224
Stock options exercised, Shares	327	327
Stock-based compensation	$ 4,280			4,280
Business acquisitions	2,857	$ 1		2,856
Business acquisitions, Shares		113
Balance, Amount at Jun. 30, 2020	695,220	$ 1,335	$ (566,762)	725,064	537,892	(2,309)
Balance, Shares at Jun. 30, 2020		133,536	78,881
Balance, Amount at Mar. 31, 2020	670,260	$ 1,332	$ (565,180)	719,616	516,424	(1,932)
Balance, Shares at Mar. 31, 2020		133,241	78,811
Net income	21,468				21,468
Other comprehensive loss	(377)					(377)
Share repurchases	(1,582)		$ (1,582)
Share repurchases, Shares			70
Restricted stock, Shares		40
Stock options exercised	2,214	$ 2		2,212
Stock options exercised, Shares		211
Stock-based compensation	2,257			2,257
Business acquisitions	980	$ 1		979
Business acquisitions, Shares		44
Balance, Amount at Jun. 30, 2020	$ 695,220	$ 1,335	$ (566,762)	$ 725,064	$ 537,892	$ (2,309)
Balance, Shares at Jun. 30, 2020		133,536	78,881