CONDENSED CONSOLIDATED STATEMENT OF CHANGES IN STOCKHOLDERS’ EQUITY - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-In Capital [Member]	Accumulated Other Comprehensive Loss [Member]	Retained Earnings [Member]
Balance at January 1, 2019	$ 2,705,714	$ 361	$ 2,339,253	$ (9,020)	$ 375,120
Balance (in shares) at Dec. 31, 2017		36,107,000
Beginning balance at Dec. 31, 2017	2,651,250	$ 361	2,339,253	(9,020)	320,656
Net income	52,231				52,231
Other comprehensive income	951			951
Exercise of stock options (in shares)		111,000
Exercise of stock options	9,328	$ 1	9,327
Restricted stock grants (in shares)		114,000
Restricted stock grants	0	$ 1	(1)
Restricted stock grants surrendered (in shares)		(47,000)
Restricted stock grants surrendered	(15,392)	$ 0	(15,392)
Stock-based compensation expense	10,335		10,335
Employee stock purchase plan (in shares)		4,000
Employee stock purchase plan	1,431	$ 0	1,431
Stock issued for acquisitions (in shares)		103,000
Stock issued for acquisitions	36,366	$ 1	36,365
Balance (in shares) at Mar. 31, 2018		36,392,000
Ending balance at Mar. 31, 2018	2,800,964	$ 364	2,381,318	(8,069)	427,351
Balance at January 1, 2019	3,033,999	$ 364	2,419,812	(11,688)	625,511
Balance (in shares) at Dec. 31, 2018		36,446,000
Beginning balance at Dec. 31, 2018	3,021,942	$ 364	2,419,812	(11,688)	613,454
Net income	85,169				85,169
Other comprehensive income	380			380
Exercise of stock options (in shares)		79,000
Exercise of stock options	10,638	$ 1	10,637
Restricted stock grants (in shares)		132,000
Restricted stock grants	0	$ 1	(1)
Restricted stock grants surrendered (in shares)		(43,000)
Restricted stock grants surrendered	(18,679)	$ 0	(18,679)
Stock-based compensation expense	12,034		12,034
Management stock purchase plan	3,491
Employee stock purchase plan (in shares)		4,000
Employee stock purchase plan	1,582	$ 0	1,582
Balance (in shares) at Mar. 31, 2019		36,618,000
Ending balance at Mar. 31, 2019	$ 3,128,614	$ 366	$ 2,428,876	$ (11,308)	$ 710,680