Condensed Consolidated Statements of Shareholders' Equity - USD ($) $ in Thousands	Total	Cumulative Effect, Period Of Adoption, Adjustment	Common Stock [Member]	Treasury Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Retained Earnings [Member] Cumulative Effect, Period Of Adoption, Adjustment	Total
Beginning balance at Dec. 31, 2019	$ 867,185	$ (18,114)	$ 281	$ (58,181)	$ 526,599	$ 380,737	$ (18,114)	$ 17,749
Net income	27,502		0	0	0	27,502		0
Other comprehensive income	15,060		0	0	0	0		15,060
Comprehensive income	42,562
Cash dividends paid on common shares	(9,458)		0	0	0	(9,458)		0
Repurchase of common stock	(15,347)		0	(15,347)	0	0		0
Issuance under equity compensation plans, net	(894)		0	0	(894)	0		0
Share-based Payment Arrangement, Noncash Expense	2,029		0	0	2,029	0		0
Ending balance at Jun. 30, 2020	867,963		281	(73,528)	527,734	380,667		32,809
Beginning balance at Mar. 31, 2020	846,436		281	(73,528)	525,838	370,748		23,097
Net income	14,634		0	0	0	14,634		0
Other comprehensive income	9,712		0	0	0	0		9,712
Comprehensive income	24,346
Cash dividends paid on common shares	(4,715)		0	0	0	(4,715)		0
Issuance under equity compensation plans, net	827		0	0	827	0		0
Share-based Payment Arrangement, Noncash Expense	1,069		0	0	1,069	0		0
Ending balance at Jun. 30, 2020	867,963		281	(73,528)	527,734	380,667		32,809
Beginning balance at Dec. 31, 2020	1,078,975		332	(73,528)	697,839	417,212		37,120
Net income	68,331		0	0	0	68,331		0
Other comprehensive income	(8,848)		0	0	0	0		(8,848)
Comprehensive income	59,483
Cash dividends paid on common shares	(11,261)		0	0	0	(11,261)		0
Repurchase of common stock	(11,833)		(2)	0	(11,831)	0		0
Issuance under equity compensation plans, net	154		0	0	154	0		0
Share-based Payment Arrangement, Noncash Expense	2,783		0	0	2,783	0		0
Ending balance at Jun. 30, 2021	1,118,301		330	(73,528)	688,945	474,282		28,272
Beginning balance at Mar. 31, 2021	1,092,497		332	(73,528)	698,005	441,511		26,177
Net income	38,405		0	0	0	38,405		0
Other comprehensive income	2,095		0	0	0	0		2,095
Comprehensive income	40,500
Cash dividends paid on common shares	(5,634)		0	0	0	(5,634)		0
Repurchase of common stock	(11,833)		(2)	0	(11,831)	0		0
Issuance under equity compensation plans, net	1,263		0	0	1,263	0		0
Share-based Payment Arrangement, Noncash Expense	1,508		0	0	1,508	0		0
Ending balance at Jun. 30, 2021	$ 1,118,301		$ 330	$ (73,528)	$ 688,945	$ 474,282		$ 28,272