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 (in 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	9,030		8,947	83
Exercise of stock options, net (in shares)		103,364
Exercise of stock options, net	(1,772)	$ 2	(1,774)
Issuance of restricted stock, net (in shares)		117,643
Issuance of restricted stock, net	(7,472)	$ 1	(7,473)
Common stock dividends	(33,367)			(33,367)
Unrealized (losses) gains on marketable securities, net of tax	415				415
Net income	52,601			52,601
Ending balance (in shares) at Sep. 30, 2019		21,964,505
Ending balance at Sep. 30, 2019	1,444,659	$ 220	1,306,353	137,639	447
Beginning balance (in shares) at Jun. 30, 2019		21,948,563
Beginning balance at Jun. 30, 2019	1,437,876	$ 219	1,305,148	132,060	449
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation	3,021		3,021
Exercise of stock options, net (in shares)		12,795
Exercise of stock options, net	(1,564)	$ 1	(1,565)
Issuance of restricted stock, net (in shares)		3,147
Issuance of restricted stock, net	(251)		(251)
Common stock dividends	(11,113)			(11,113)
Unrealized (losses) gains on marketable securities, net of tax	(2)				(2)
Net income	16,692			16,692
Ending balance (in shares) at Sep. 30, 2019		21,964,505
Ending balance at Sep. 30, 2019	1,444,659	$ 220	1,306,353	137,639	447
Beginning balance (in 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]
Issuance of common stock (in shares)		2,185,000
Issuance of common stock in public offering	220,248	$ 22	220,226
Stock-based compensation	10,759		10,743	16
Exercise of stock options, net (in shares)		19,810
Exercise of stock options, net	1,207		1,207
Issuance of restricted stock, net (in shares)		235,514
Issuance of restricted stock, net	(25,845)	$ 2	(25,847)
Repurchase of common stock (in shares)		(1,769)
Repurchase of common stock	(247)		(105)	(142)
Common stock dividends	(41,341)			(41,341)
Unrealized (losses) gains on marketable securities, net of tax	527				527
Net income	80,351			80,351
Ending balance (in shares) at Sep. 30, 2020		24,403,364
Ending balance at Sep. 30, 2020	1,705,058	$ 244	1,515,662	188,392	760
Beginning balance (in shares) at Jun. 30, 2020		22,222,936
Beginning balance at Jun. 30, 2020	1,484,550	$ 222	1,291,597	192,072	659
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock (in shares)		2,185,000
Issuance of common stock in public offering	220,248	$ 22	220,226
Stock-based compensation	3,875		3,860	15
Exercise of stock options, net (in shares)		243
Exercise of stock options, net	21		21
Issuance of restricted stock, net (in shares)		(4,815)
Issuance of restricted stock, net	(42)		(42)
Common stock dividends	(14,655)			(14,655)
Unrealized (losses) gains on marketable securities, net of tax	101				101
Net income	10,960			10,960
Ending balance (in shares) at Sep. 30, 2020		24,403,364
Ending balance at Sep. 30, 2020	$ 1,705,058	$ 244	$ 1,515,662	$ 188,392	$ 760