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 (loss)	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, 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	52,130
Other comprehensive income (loss)	17,186
Comprehensive income	69,316
Ending balance (in shares) at Sep. 30, 2020			56,193,705
Ending balance at Sep. 30, 2020	2,104,300		$ 296,483	(101,800)	1,294,888	596,779		17,950
Beginning balance (in shares) at Mar. 31, 2020			56,141,018
Beginning balance at Mar. 31, 2020	2,070,512		$ 296,483	(103,620)	1,291,439	571,709		14,501
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	20,130					20,130
Other comprehensive income (loss)	1,838							1,838
Comprehensive income	21,968
Cash dividends	(12,525)					(12,525)
Issuance of common stock for stock-based compensation awards (in shares)			40,944
Issuance of common stock for stock-based compensation awards	(7)			1,397	(1,404)
Stock-based compensation expense	2,998				2,998
Ending balance (in shares) at Jun. 30, 2020			56,181,962
Ending balance at Jun. 30, 2020	2,082,946		$ 296,483	(102,223)	1,293,033	579,314		16,339
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	29,992					29,992
Other comprehensive income (loss)	1,611							1,611
Comprehensive income	31,603
Cash dividends	(12,527)					(12,527)
Issuance of common stock for stock-based compensation awards (in shares)			11,743
Issuance of common stock for stock-based compensation awards	(127)			423	(550)
Stock-based compensation expense	2,405				2,405
Ending balance (in shares) at Sep. 30, 2020			56,193,705
Ending balance at Sep. 30, 2020	2,104,300		$ 296,483	(101,800)	1,294,888	596,779		17,950
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 (loss)	(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
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	138,838
Other comprehensive income (loss)	(14,374)
Comprehensive income	124,464
Ending balance (in shares) at Sep. 30, 2021			55,747,407
Ending balance at Sep. 30, 2021	2,203,944		$ 296,483	(118,288)	1,298,022	717,033		10,694
Beginning balance (in shares) at Mar. 31, 2021			56,294,346
Beginning balance at Mar. 31, 2021	2,173,701		$ 296,483	(98,949)	1,294,911	661,117		20,139
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	40,867					40,867
Other comprehensive income (loss)	(889)							(889)
Comprehensive income	39,978
Cash dividends	(12,540)					(12,540)
Issuance of common stock for stock-based compensation awards (in shares)			56,532
Issuance of common stock for stock-based compensation awards	283			1,700	(1,417)
Stock-based compensation expense	2,385				2,385
Ending balance (in shares) at Jun. 30, 2021			56,350,878
Ending balance at Jun. 30, 2021	2,203,807		$ 296,483	(97,249)	1,295,879	689,444		19,250
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	40,063					40,063
Other comprehensive income (loss)	(8,556)							(8,556)
Comprehensive income	31,507
Cash dividends	(12,474)					(12,474)
Repurchase of shares in connection with stock repurchase program (in shares)			(612,107)
Repurchase of shares in connection with stock repurchase program	(21,314)			(21,314)
Issuance of common stock for stock-based compensation awards (in shares)			8,636
Issuance of common stock for stock-based compensation awards	(176)			275	(451)
Stock-based compensation expense	2,594				2,594
Ending balance (in shares) at Sep. 30, 2021			55,747,407
Ending balance at Sep. 30, 2021	$ 2,203,944		$ 296,483	$ (118,288)	$ 1,298,022	$ 717,033		$ 10,694