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, 2018		29,725,000
Beginning balance at Dec. 31, 2018	$ 764,230	$ 434,453	$ 341,738	$ (3,235)	$ 3,235	$ (11,961)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
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 earnout (in shares)		78,000
Equity issued related to acquisition earnout	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 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		29,717,000
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)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
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 earnout (in shares)		78,000
Equity issued related to acquisition earnout	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 withheld for payment of taxes (in shares)		0
Stock withheld for payment of taxes	0	$ 0
Stock-based compensation (in shares)		66,000
Stock-based compensation	910	$ 910
Other comprehensive income (loss)	9,152					9,152
Ending balance (in shares) at Jun. 30, 2019		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 Dec. 31, 2019	29,601,264	29,601,000
Beginning balance at Dec. 31, 2019	$ 852,401	$ 429,514	417,764	(2,587)	2,587	5,123
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	34,532		34,532
Cash dividends declared	(10,450)		(10,450)
Change in Rabbi Trust Obligation	0			370	(370)
Stock repurchased (in shares)		(680,000)
Stock repurchases	(22,432)	$ (22,432)
Stock-based compensation (in shares)		56,000
Stock-based compensation	1,617	$ 1,617
Other comprehensive income (loss)	$ 12,223					12,223
Ending balance (in shares) at Jun. 30, 2020	28,976,681	28,977,000
Ending balance at Jun. 30, 2020	$ 867,891	$ 408,699	441,846	(2,217)	2,217	17,346
Beginning balance (in shares) at Mar. 31, 2020		29,041,000
Beginning balance at Mar. 31, 2020	862,198	$ 410,236	430,709	(2,602)	2,602	21,253
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	16,352		16,352
Cash dividends declared	(5,215)		(5,215)
Change in Rabbi Trust Obligation	0			385	(385)
Stock repurchased (in shares)		(104,000)
Stock repurchases	(2,432)	$ (2,432)
Stock-based compensation (in shares)		40,000
Stock-based compensation	895	$ 895
Other comprehensive income (loss)	$ (3,907)					(3,907)
Ending balance (in shares) at Jun. 30, 2020	28,976,681	28,977,000
Ending balance at Jun. 30, 2020	$ 867,891	$ 408,699	$ 441,846	$ (2,217)	$ 2,217	$ 17,346