Consolidated Statements of Changes in Stockholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Cumulative effect of newly adopted accounting standards	Cumulative Effect, Period of Adoption, Adjusted Balance	Common Stock	Common Stock Cumulative Effect, Period of Adoption, Adjusted Balance	Additional Paid-in Capital	Additional Paid-in Capital Cumulative Effect, Period of Adoption, Adjusted Balance	Retained Earnings	Retained Earnings Cumulative effect of newly adopted accounting standards	Retained Earnings Cumulative Effect, Period of Adoption, Adjusted Balance
Beginning balance (in shares) at Dec. 31, 2019				62,574,961	62,574,961
Beginning balance at Dec. 31, 2019	$ 1,782,485	$ (34)	$ 1,782,451	$ 626	$ 626	$ 1,348,733	$ 1,348,733	$ 433,126	$ (34)	$ 433,092
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	36,760							36,760
Shares issued under stock-based compensation programs, net (in shares)				477,582
Shares issued under stock-based compensation programs, net	8,194			$ 5		8,189
Cash dividends declared	(20,768)							(20,768)
Stock-based compensation expense	4,440					4,440
Forfeiture of restricted stock (in shares)				(48)
Ending balance (in shares) at Mar. 31, 2020				63,052,495
Ending balance at Mar. 31, 2020	1,811,077			$ 631		1,361,362		449,084
Beginning balance (in shares) at Dec. 31, 2019				62,574,961	62,574,961
Beginning balance at Dec. 31, 2019	1,782,485	$ (34)	$ 1,782,451	$ 626	$ 626	1,348,733	$ 1,348,733	433,126	$ (34)	$ 433,092
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	220,094
Ending balance (in shares) at Sep. 30, 2020				64,865,577
Ending balance at Sep. 30, 2020	1,987,999			$ 649		1,397,220		590,130
Beginning balance (in shares) at Mar. 31, 2020				63,052,495
Beginning balance at Mar. 31, 2020	1,811,077			$ 631		1,361,362		449,084
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	84,396							84,396
Shares issued under stock-based compensation programs, net (in shares)				334,178
Shares issued under stock-based compensation programs, net	(6,862)			$ 3		(6,865)
Cash dividends declared	(20,914)							(20,914)
Stock-based compensation expense	5,488					5,488
Forfeiture of restricted stock (in shares)				(1,807)
Ending balance (in shares) at Jun. 30, 2020				63,384,866
Ending balance at Jun. 30, 2020	1,873,185			$ 634		1,359,985		512,566
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	98,938							98,938
Shares issued under stock-based compensation programs, net (in shares)				1,480,711
Shares issued under stock-based compensation programs, net	28,642			$ 15		28,627
Cash dividends declared	(21,374)							(21,374)
Stock-based compensation expense	8,608					8,608
Ending balance (in shares) at Sep. 30, 2020				64,865,577
Ending balance at Sep. 30, 2020	$ 1,987,999			$ 649		1,397,220		590,130
Beginning balance (in shares) at Dec. 31, 2020	64,851,126			64,851,126
Beginning balance at Dec. 31, 2020	$ 2,119,912			$ 649		1,407,597		711,666
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	110,690							110,690
Shares issued under stock-based compensation programs, net (in shares)				221,303
Shares issued under stock-based compensation programs, net	1,009			$ 2		1,007
Cash dividends declared	(25,978)							(25,978)
Stock dividend declared (in shares)				5,192,776
Stock dividend declared	(687)			$ 52		279,579		(280,318)
Stock-based compensation expense	9,926					9,926
Ending balance (in shares) at Mar. 31, 2021				70,265,205
Ending balance at Mar. 31, 2021	$ 2,214,872			$ 703		1,698,109		516,060
Beginning balance (in shares) at Dec. 31, 2020	64,851,126			64,851,126
Beginning balance at Dec. 31, 2020	$ 2,119,912			$ 649		1,407,597		711,666
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	$ 410,996
Ending balance (in shares) at Sep. 30, 2021	70,679,612			70,679,612
Ending balance at Sep. 30, 2021	$ 2,457,984			$ 707		1,697,435		759,842
Beginning balance (in shares) at Mar. 31, 2021				70,265,205
Beginning balance at Mar. 31, 2021	2,214,872			$ 703		1,698,109		516,060
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	154,352							154,352
Shares issued under stock-based compensation programs, net (in shares)				358,993
Shares issued under stock-based compensation programs, net	(16,543)			$ 3		(16,546)
Cash dividends declared	(28,248)							(28,248)
Stock-based compensation expense	8,126					8,126
Forfeiture of restricted stock (in shares)				(4,560)
Ending balance (in shares) at Jun. 30, 2021				70,619,638
Ending balance at Jun. 30, 2021	2,332,559			$ 706		1,689,689		642,164
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	145,954							145,954
Shares issued under stock-based compensation programs, net (in shares)				69,512
Shares issued under stock-based compensation programs, net	(19)			$ 1		(20)
Cash dividends declared	(28,276)							(28,276)
Stock-based compensation expense	$ 7,766					7,766
Forfeiture of restricted stock (in shares)				(9,538)
Ending balance (in shares) at Sep. 30, 2021	70,679,612			70,679,612
Ending balance at Sep. 30, 2021	$ 2,457,984			$ 707		$ 1,697,435		$ 759,842