Consolidated Statements of Shareholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Retained Earnings	Stock in Rabbi Trust Assumed in Acquisition	Rabbi Trust Obligation	Accumulated Other Comprehensive Income (Loss)
Beginning balance (in shares) at Dec. 31, 2017		29,639,000
Beginning balance at Dec. 31, 2017	$ 692,979	$ 432,794	$ 264,331	$ (3,581)	$ 3,581	$ (4,146)
Net income	43,403		43,403
Cash dividends declared	(5,934)		(5,934)
Change in Rabbi Trust Obligation	0			367	(367)
Stock option exercises (in shares)		25,000
Stock option exercises	324	$ 324
Stock withheld for payment of taxes (in shares)		(4,000)
Stock withheld for payment of taxes	0	$ 0
Stock-based compensation (in shares)		43,000
Stock-based compensation	999	$ 999
Other comprehensive income (loss)	$ (7,049)					(7,049)
Ending balance (in shares) at Jun. 30, 2018	29,702,912	29,703,000
Ending balance at Jun. 30, 2018	$ 724,722	$ 434,117	301,800	(3,214)	3,214	(11,195)
Beginning balance (in shares) at Mar. 31, 2018		29,661,000
Beginning balance at Mar. 31, 2018	705,650	$ 433,305	282,038	(3,588)	3,588	(9,693)
Net income	22,730		22,730
Cash dividends declared	(2,968)		(2,968)
Change in Rabbi Trust Obligation	0			374	(374)
Stock option exercises (in shares)		17,000
Stock option exercises	216	$ 216
Stock withheld for payment of taxes (in shares)		(4,000)
Stock withheld for payment of taxes	0	$ 0
Stock-based compensation (in shares)		29,000
Stock-based compensation	596	$ 596
Other comprehensive income (loss)	$ (1,502)					(1,502)
Ending balance (in shares) at Jun. 30, 2018	29,702,912	29,703,000
Ending balance at Jun. 30, 2018	$ 724,722	$ 434,117	301,800	(3,214)	3,214	(11,195)
Beginning balance (in shares) at Dec. 31, 2018	29,724,874	29,725,000
Beginning balance at Dec. 31, 2018	$ 764,230	$ 434,453	341,738	(3,235)	3,235	(11,961)
Net income	46,144		46,144
Cash dividends declared	(7,134)		(7,134)
Change in Rabbi Trust Obligation	0			369	(369)
Equity issued related to acquisition earn-out (in shares)		78,000
Equity issued related to acquisition earn-out	3,070	$ 3,070
Stock repurchased (in shares)		(182,000)
Stock repurchases	$ (6,524)	$ (6,524)
Stock option exercises (in shares)	9,000	9,000
Stock option exercises	$ 129	$ 129
Stock withheld for payment of taxes (in shares)		(2,000)
Stock withheld for payment of taxes	(91)	$ (91)
Stock-based compensation (in shares)		89,000
Stock-based compensation	1,496	$ 1,496
Other comprehensive income (loss)	$ 13,849					13,849
Ending balance (in shares) at Jun. 30, 2019	29,717,223	29,717,000
Ending balance at Jun. 30, 2019	$ 815,169	$ 432,533	380,748	(2,866)	2,866	1,888
Beginning balance (in shares) at Mar. 31, 2019		29,746,000
Beginning balance at Mar. 31, 2019	788,139	$ 434,948	360,455	(3,245)	3,245	(7,264)
Net income	23,859		23,859
Cash dividends declared	(3,566)		(3,566)
Change in Rabbi Trust Obligation	0			379	(379)
Equity issued related to acquisition earn-out (in shares)		78,000
Equity issued related to acquisition earn-out	3,070	$ 3,070
Stock repurchased (in shares)		(182,000)
Stock repurchases	(6,524)	$ (6,524)
Stock option exercises (in shares)		9,000
Stock option exercises	129	$ 129
Stock-based compensation (in shares)		65,000
Stock-based compensation	910	$ 910
Other comprehensive income (loss)	$ 9,152					9,152
Ending balance (in shares) at Jun. 30, 2019	29,717,223	29,717,000
Ending balance at Jun. 30, 2019	$ 815,169	$ 432,533	$ 380,748	$ (2,866)	$ 2,866	$ 1,888