CONDENSED CONSOLIDATED STATEMENT OF CHANGES IN STOCKHOLDERS’ EQUITY - USD ($) shares in Thousands, $ in Thousands	Total	Cumulative Effect, Period of Adoption, Adjustment	Cumulative Effect, Period of Adoption, Adjusted Balance	Common Stock [Member]	Common Stock [Member] Cumulative Effect, Period of Adoption, Adjusted Balance	Additional Paid-In Capital [Member]	Additional Paid-In Capital [Member] Cumulative Effect, Period of Adoption, Adjusted Balance	Accumulated Other Comprehensive Loss [Member]	Accumulated Other Comprehensive Loss [Member] Cumulative Effect, Period of Adoption, Adjusted Balance	Retained Earnings [Member]	Retained Earnings [Member] Cumulative Effect, Period of Adoption, Adjustment	Retained Earnings [Member] Cumulative Effect, Period of Adoption, Adjusted Balance
Balance (in shares) at Dec. 31, 2018				36,446
Beginning Balance at Dec. 31, 2018	$ 3,021,942	$ 12,057	$ 3,033,999	$ 364	$ 364	$ 2,419,812	$ 2,419,812	$ (11,688)	$ (11,688)	$ 613,454	$ 12,057	$ 625,511
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					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, 2018				36,446
Beginning Balance at Dec. 31, 2018	3,021,942	$ 12,057	$ 3,033,999	$ 364	$ 364	2,419,812	$ 2,419,812	(11,688)	$ (11,688)	613,454	$ 12,057	$ 625,511
Net income	148,417
Other comprehensive income (loss)	(387)
Balance (in shares) at Jun. 30, 2019				36,624
Ending Balance at Jun. 30, 2019	3,204,071			$ 366		2,441,852		(12,075)		773,928
Balance (in shares) at Mar. 31, 2019				36,618
Beginning Balance at Mar. 31, 2019	3,128,614			$ 366		2,428,876		(11,308)		710,680
Net income	63,248									63,248
Other comprehensive income (loss)	(767)							(767)
Exercise of stock options (in shares)				15
Exercise of stock options	3,001					3,001
Restricted stock grants (in shares)				4
Restricted stock grants	0
Restricted stock grants surrendered (in shares)				(17)
Restricted stock grants surrendered	(5,546)					(5,546)
Stock-based compensation expense	13,706					13,706
Employee stock purchase plan (in shares)				4
Employee stock purchase plan	1,815					1,815
Balance (in shares) at Jun. 30, 2019				36,624
Ending Balance at Jun. 30, 2019	3,204,071			$ 366		2,441,852		(12,075)		773,928
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					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
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	133,153
Other comprehensive income (loss)	(11,356)
Balance (in shares) at Jun. 30, 2020				39,383
Ending Balance at Jun. 30, 2020	5,224,321			$ 393		4,170,242		(19,941)		1,073,627
Balance (in shares) at Mar. 31, 2020				36,740
Beginning Balance at Mar. 31, 2020	3,462,811			$ 367		2,469,981		(20,804)		1,013,267
Net income	60,360									60,360
Other comprehensive income (loss)	863							863
Exercise of stock options (in shares)				11
Exercise of stock options	2,924					2,924
Restricted stock grants (in shares)				11
Restricted stock grants	0					0
Restricted stock grants surrendered (in shares)				(17)
Restricted stock grants surrendered	(3,509)					(3,509)
Stock-based compensation expense	8,609					8,609
Employee stock purchase plan (in shares)				4
Employee stock purchase plan	2,292					2,292
Stock issued for equity offering (in shares)				2,634
Stock issued for equity offering, net of transaction costs	1,689,971			$ 26		1,689,945
Balance (in shares) at Jun. 30, 2020				39,383
Ending Balance at Jun. 30, 2020	$ 5,224,321			$ 393		$ 4,170,242		$ (19,941)		$ 1,073,627