Condensed Consolidated Statements of Shareholders' Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Treasury Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	AOCI Attributable to Parent [Member]
Balance at Dec. 31, 2017	$ 548,573	$ 238	$ (23,268)	$ 350,061	$ 225,360	$ (3,818)
Net income	65,688	0	0	0	65,688	0
Other comprehensive income	(11,975)	0	0	0	0	(11,975)
Total comprehensive income	53,713	0	0	0	65,688	(11,975)
Cash dividends paid on common shares	(7,866)	0	0	0	(7,866)	0
Repurchase of common stock	(6,840)	0	(6,840)	0	0	0
Issuance under equity compensation plans, net	(3,297)	1	0	(3,298)	0	0
Share-based Payment Arrangement, Noncash Expense	2,554	0	0	2,554	0	0
Reclassification for the adoption of new accounting standards	0	0	0	0	834	(834)
Balance at Sep. 30, 2018	586,837	239	(30,108)	349,317	284,016	(16,627)
Balance at Jun. 30, 2018	574,084	239	(26,326)	348,471	264,280	(12,580)
Net income	22,516	0	0	0	22,516	0
Other comprehensive income	(4,047)	0	0	0	0	(4,047)
Total comprehensive income	18,469	0	0	0	22,516	(4,047)
Cash dividends paid on common shares	(2,780)	0	0	0	2,780	0
Repurchase of common stock	3,782	0	3,782	0	0	0
Issuance under equity compensation plans, net	(77)	0	0	(77)	0	0
Share-based Payment Arrangement, Noncash Expense	923	0	0	923	0	0
Balance at Sep. 30, 2018	586,837	239	(30,108)	349,317	284,016	(16,627)
Balance at Dec. 31, 2018	603,804	239	(42,655)	350,936	304,566	(9,282)
Net income	63,649	0	0	0	63,649	0
Other comprehensive income	28,493	0	0	0	0	28,493
Total comprehensive income	92,142	0	0	0	63,649	28,493
Cash dividends paid on common shares	(12,055)	0	0	0	(12,055)	0
Repurchase of common stock	(11,817)	0	(11,817)	0	0	0
Issuance under equity compensation plans, net	(880)	1	0	(881)	0	0
Share-based Payment Arrangement, Noncash Expense	3,016	0	0	3,016	0	0
Shares issued in connection with acquisition	171,885	40	0	171,845	0	0
Balance at Sep. 30, 2019	846,095	280	(54,472)	524,916	356,160	19,211
Balance at Jun. 30, 2019	825,501	280	(42,655)	523,454	331,348	13,074
Net income	29,069	0	0	0	29,069	0
Other comprehensive income	6,137	0	0	0	0	6,137
Total comprehensive income	35,206	0	0	0	29,069	6,137
Cash dividends paid on common shares	(4,257)	0	0	0	(4,257)	0
Repurchase of common stock	(11,817)	0	(11,817)	0	0	0
Issuance under equity compensation plans, net	353	0	0	353	0	0
Share-based Payment Arrangement, Noncash Expense	1,109	0	0	1,109	0	0
Balance at Sep. 30, 2019	$ 846,095	$ 280	$ (54,472)	$ 524,916	$ 356,160	$ 19,211