UNAUDITED CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERSEQUITY - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Income	Cumulative Effect Period of Adoption Adjustment	Cumulative Effect Period of Adoption Adjustment Retained Earnings
Beginning balance, shares at Dec. 31, 2018		21,743,498
Beginning balance at Dec. 31, 2018	$ 1,425,224	$ 217	$ 1,306,653	$ 118,322	$ 32
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation	6,008		5,926	82
Exercise of stock options, net (in shares)		90,569
Exercise of stock options, net	(208)	$ 1	(209)
Issuance of restricted stock, net (in shares)		114,496
Issuance of restricted stock, net	(7,221)	$ 1	(7,222)
Common stock dividends	(22,253)			(22,253)
Unrealized gains on marketable securities, net of tax	417				417
Net income	35,909			35,909
Ending balance, shares at Jun. 30, 2019		21,948,563
Ending balance at Jun. 30, 2019	1,437,876	$ 219	1,305,148	132,060	449
Beginning balance, shares at Mar. 31, 2019		21,923,800
Beginning balance at Mar. 31, 2019	1,423,438	$ 219	1,304,170	118,783	266
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation	3,155		3,155
Exercise of stock options, net (in shares)		38,680
Exercise of stock options, net	1,491		1,491
Issuance of restricted stock, net (in shares)		(13,917)
Issuance of restricted stock, net	(3,668)		(3,668)
Common stock dividends	(11,132)			(11,132)
Unrealized gains on marketable securities, net of tax	183				183
Net income	24,409			24,409
Ending balance, shares at Jun. 30, 2019		21,948,563
Ending balance at Jun. 30, 2019	1,437,876	$ 219	1,305,148	132,060	449
Beginning balance, shares at Dec. 31, 2019		21,964,809
Beginning balance at Dec. 31, 2019	1,462,710	$ 220	1,309,438	152,819	233	$ (3,311)	$ (3,311)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation	6,884		6,883	1
Exercise of stock options, net (in shares)		19,567
Exercise of stock options, net	1,185		1,185
Issuance of restricted stock, net (in shares)		240,329
Issuance of restricted stock, net	(25,802)	$ 2	(25,804)
Repurchase of common stock (in shares)		(1,769)
Repurchase of common stock	(247)		(105)	(142)
Common stock dividends	(26,686)			(26,686)
Unrealized gains on marketable securities, net of tax	426				426
Net income	69,391			69,391
Ending balance, shares at Jun. 30, 2020		22,222,936
Ending balance at Jun. 30, 2020	1,484,550	$ 222	1,291,597	192,072	659
Beginning balance, shares at Mar. 31, 2020		22,213,587
Beginning balance at Mar. 31, 2020	1,459,147	$ 222	1,287,406	171,266	253
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation	3,859		3,858	1
Exercise of stock options, net (in shares)		5,252
Exercise of stock options, net	339		339
Issuance of restricted stock, net (in shares)		4,097
Issuance of restricted stock, net	(6)		(6)
Common stock dividends	(13,347)			(13,347)
Unrealized gains on marketable securities, net of tax	406				406
Net income	34,152			34,152
Ending balance, shares at Jun. 30, 2020		22,222,936
Ending balance at Jun. 30, 2020	$ 1,484,550	$ 222	$ 1,291,597	$ 192,072	$ 659