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	36,848				36,848
Other comprehensive income (loss)	(1,252)					(1,252)
Share repurchases (in shares)			1,174
Share repurchases	(29,487)		$ (29,487)
Stock options exercised (in shares)		116
Stock options exercised	1,013	$ 1		1,012
Stock-based compensation	2,023			2,023
Business acquisitions (in shares)		69
Business acquisitions	1,877			1,877
Ending balance (in shares) at Mar. 31, 2020		133,241	78,811
Ending balance at Mar. 31, 2020	670,260	$ 1,332	$ (565,180)	719,616	516,424	(1,932)
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	50,209				50,209
Other comprehensive income (loss)	854					854
Share repurchases (in shares)			1,164
Share repurchases	(34,142)		$ (34,142)
Restricted stock units and awards (in shares)		46
Restricted stock units and awards	$ 0	$ 1		(1)
Stock options exercised (in shares)	397	397
Stock options exercised	$ 4,408	$ 4		4,404
Stock-based compensation	2,855			2,855
Business acquisitions (in shares)		38
Business acquisitions	979			979
Ending balance (in shares) at Mar. 31, 2021		134,625	81,209
Ending balance at Mar. 31, 2021	$ 727,783	$ 1,346	$ (629,439)	$ 749,207	$ 608,084	$ (1,415)