CONDENSED CONSOLIDATED STATEMENT OF CHANGES IN STOCKHOLDERS’ EQUITY - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock [Member]	Additional Paid-In Capital [Member]	Accumulated Other Comprehensive Loss [Member]	Retained Earnings [Member]
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
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 (loss)	380			380
Exercise of stock options (in shares)		79
Exercise of stock options	10,638	$ 1	10,637
Restricted stock grants (in shares)		132
Restricted stock grants	0	$ 1	(1)
Restricted stock grants surrendered (in shares)		(43)
Restricted stock grants surrendered	(18,679)		(18,679)
Stock-based compensation expense	12,034		12,034
Management stock purchase plan	3,491		3,491
Employee stock purchase plan (in shares)		4
Employee stock purchase plan	1,582	$ 0	1,582
Balance (in shares) at Mar. 31, 2019		36,618
Ending balance at Mar. 31, 2019	3,128,614	$ 366	2,428,876	(11,308)	710,680
Balance (in shares) at Dec. 31, 2019		36,668
Beginning balance at Dec. 31, 2019	3,405,593	$ 366	2,473,338	(8,585)	940,474
Net income	72,793				72,793
Other comprehensive income (loss)	(12,219)			(12,219)
Exercise of stock options (in shares)		41
Exercise of stock options	9,233	$ 1	9,232
Restricted stock grants (in shares)		83
Restricted stock grants	0	$ 1	(1)
Restricted stock grants surrendered (in shares)		(56)
Restricted stock grants surrendered	(30,145)	$ (1)	(30,144)
Stock-based compensation expense	15,006		15,006
Employee stock purchase plan (in shares)		4
Employee stock purchase plan	2,550	$ 0	2,550
Balance (in shares) at Mar. 31, 2020		36,740
Ending balance at Mar. 31, 2020	$ 3,462,811	$ 367	$ 2,469,981	$ (20,804)	$ 1,013,267