Consolidated Statements of Changes in Shareholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Cumulative Effect, Period Of Adoption, Adjustment	Common Stock	Treasury Stock	Additional Paid-In Capital	Retained Earnings	Retained Earnings Cumulative Effect, Period Of Adoption, Adjustment	Accumulated Other Comprehensive Income (Loss)
Beginning balance (in shares) at Dec. 31, 2019			56,855,002
Beginning balance at Dec. 31, 2019	$ 2,125,689	$ (35,099)	$ 296,483	$ (83,189)	$ 1,294,276	$ 617,355	$ (35,099)	$ 764
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	2,008					2,008
Other comprehensive income	13,737							13,737
Comprehensive income	15,745
Cash dividends	(12,555)					(12,555)
Repurchase of shares in connection with stock repurchase program (in shares)			(818,886)
Repurchase of shares in connection with stock repurchase program	(24,569)			(24,569)
Issuance of common stock for stock-based compensation awards (in shares)			104,902
Issuance of common stock for stock-based compensation awards	(1,449)			4,138	(5,587)
Stock-based compensation expense	2,750				2,750
Ending balance (in shares) at Mar. 31, 2020			56,141,018
Ending balance at Mar. 31, 2020	2,070,512		$ 296,483	(103,620)	1,291,439	571,709		14,501
Beginning balance (in shares) at Dec. 31, 2020			56,200,487
Beginning balance at Dec. 31, 2020	2,132,733		$ 296,483	(101,554)	1,296,963	615,773		25,068
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	57,908					57,908
Other comprehensive income	(4,929)							(4,929)
Comprehensive income	52,979
Cash dividends	(12,564)					(12,564)
Issuance of common stock for stock-based compensation awards (in shares)			93,859
Issuance of common stock for stock-based compensation awards	(2,203)			2,605	(4,808)
Stock-based compensation expense	2,756				2,756
Ending balance (in shares) at Mar. 31, 2021			56,294,346
Ending balance at Mar. 31, 2021	$ 2,173,701		$ 296,483	$ (98,949)	$ 1,294,911	$ 661,117		$ 20,139