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	65,394		65,394
Cash dividends declared	(8,903)		(8,903)
Change in Rabbi Trust Obligation	0			357	(357)
Stock option exercises (in shares)		25,000
Stock option exercises	324	$ 324
Stock withheld for payment of taxes (in shares)		(7,000)
Stock withheld for payment of taxes	(264)	$ (264)
Stock-based compensation (in shares)		72,000
Stock-based compensation	1,373	$ 1,373
Other comprehensive income (loss)	(7,827)					(7,827)
Ending balance at Sep. 30, 2018	743,076	$ 434,227	320,822	(3,224)	3,224	(11,973)
Beginning balance (in shares) at Jun. 30, 2018		29,703,000
Beginning balance at Jun. 30, 2018	724,722	$ 434,117	301,800	(3,214)	3,214	(11,195)
Net income	21,991		21,991
Cash dividends declared	(2,969)		(2,969)
Change in Rabbi Trust Obligation	0			(10)	10
Stock option exercises (in shares)		0
Stock option exercises	0	$ 0
Stock withheld for payment of taxes (in shares)		(3,000)
Stock withheld for payment of taxes	(264)	$ (264)
Stock-based compensation (in shares)		29,000
Stock-based compensation	374	$ 374
Other comprehensive income (loss)	(778)					(778)
Ending balance at Sep. 30, 2018	$ 743,076	$ 434,227	320,822	(3,224)	3,224	(11,973)
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	71,163		71,163
Cash dividends declared	(10,689)		(10,689)
Change in Rabbi Trust Obligation	0			658	(658)
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)		(282,000)
Stock repurchases	$ (10,000)	$ (10,000)
Stock option exercises (in shares)	9,000	9,000
Stock option exercises	$ 129	$ 129
Stock withheld for payment of taxes (in shares)		(15,000)
Stock withheld for payment of taxes	(558)	$ (558)
Stock-based compensation (in shares)		90,000
Stock-based compensation	2,042	$ 2,042
Other comprehensive income (loss)	$ 15,595					15,595
Ending balance (in shares) at Sep. 30, 2019	29,604,830	29,605,000
Ending balance at Sep. 30, 2019	$ 834,982	$ 429,136	402,212	(2,577)	2,577	3,634
Beginning balance (in shares) at Jun. 30, 2019		29,717,000
Beginning balance at Jun. 30, 2019	815,169	$ 432,533	380,748	(2,866)	2,866	1,888
Net income	25,019		25,019
Cash dividends declared	(3,555)		(3,555)
Change in Rabbi Trust Obligation	0			289	(289)
Equity issued related to acquisition earn-out (in shares)		0
Equity issued related to acquisition earn-out	0	$ 0
Stock repurchased (in shares)		(100,000)
Stock repurchases	(3,476)	$ (3,476)
Stock option exercises (in shares)		0
Stock option exercises	0	$ 0
Stock withheld for payment of taxes (in shares)		(12,000)
Stock withheld for payment of taxes	(467)	$ (467)
Stock-based compensation (in shares)		0
Stock-based compensation	546	$ 546
Other comprehensive income (loss)	$ 1,746					1,746
Ending balance (in shares) at Sep. 30, 2019	29,604,830	29,605,000
Ending balance at Sep. 30, 2019	$ 834,982	$ 429,136	$ 402,212	$ (2,577)	$ 2,577	$ 3,634