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
Beginning balance (in shares) at Dec. 31, 2018			58,546,480
Beginning balance at Dec. 31, 2018	$ 2,043,913		$ 296,483	$ (24,245)	$ 1,288,911	$ 500,660		$ (17,896)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	45,110					45,110
Other comprehensive income	10,446							10,446
Comprehensive income	55,556
Cash dividends	(12,442)					(12,442)
Issuance of common stock for stock-based compensation awards (in shares)			87,150
Issuance of common stock for stock-based compensation awards	(787)			2,655	(3,442)
Stock-based compensation expense	2,637				2,637
Ending balance (in shares) at Mar. 31, 2019			58,633,630
Ending balance at Mar. 31, 2019	2,088,877		$ 296,483	(21,590)	1,288,106	533,328		(7,450)
Beginning balance (in shares) at Dec. 31, 2018			58,546,480
Beginning balance at Dec. 31, 2018	2,043,913		$ 296,483	(24,245)	1,288,911	500,660		(17,896)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	91,735
Other comprehensive income	18,406
Comprehensive income	110,141
Ending balance (in shares) at Jun. 30, 2019			58,297,670
Ending balance at Jun. 30, 2019	2,119,696		$ 296,483	(33,635)	1,289,356	566,982		510
Beginning balance (in shares) at Dec. 31, 2018			58,546,480
Beginning balance at Dec. 31, 2018	$ 2,043,913		$ 296,483	(24,245)	1,288,911	500,660		(17,896)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Accounting standards update [Extensible List]	us-gaap:AccountingStandardsUpdate201613Member
Ending balance (in shares) at Dec. 31, 2019			56,855,002
Ending balance at Dec. 31, 2019	$ 2,125,689	$ (35,099)	$ 296,483	(83,189)	1,294,276	617,355	$ (35,099)	764
Beginning balance (in shares) at Mar. 31, 2019			58,633,630
Beginning balance at Mar. 31, 2019	2,088,877		$ 296,483	(21,590)	1,288,106	533,328		(7,450)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	46,625					46,625
Other comprehensive income	7,960							7,960
Comprehensive income	54,585
Cash dividends	(12,971)					(12,971)
Repurchase of shares in connection with stock repurchase program (in shares)			(363,704)
Repurchase of shares in connection with stock repurchase program	(12,938)			(12,938)
Issuance of common stock for stock-based compensation awards (in shares)			27,744
Issuance of common stock for stock-based compensation awards	61			893	(832)
Stock-based compensation expense	2,082				2,082
Ending balance (in shares) at Jun. 30, 2019			58,297,670
Ending balance at Jun. 30, 2019	2,119,696		$ 296,483	(33,635)	1,289,356	566,982		510
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, 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	22,138
Other comprehensive income	15,575
Comprehensive income	37,713
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
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	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