Consolidated Statements of Shareholders' Equity - USD ($) $ in Thousands	Total	Cumulative Effect, Period Of Adoption, Adjustment	Common Stock	Retained Earnings	Retained Earnings Cumulative Effect, Period Of Adoption, Adjustment	Stock in Rabbi Trust Assumed in Acquisition	Rabbi Trust Obligation	Accumulated Other Comprehensive Income (Loss)
Beginning balance (in shares) at Dec. 31, 2019			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	18,180			18,180
Cash dividends declared	(5,235)			(5,235)
Change in Rabbi Trust obligation	0					(15)	15
Stock repurchases (in shares)			(576,000)
Stock repurchases	(20,000)		$ (20,000)
Stock-based compensation (in shares)			16,000
Stock-based compensation	722		$ 722
Other comprehensive income (loss)	16,130							16,130
Ending balance (in shares) at Mar. 31, 2020			29,041,000
Ending balance at Mar. 31, 2020	862,198		$ 410,236	430,709		(2,602)	2,602	21,253
Beginning balance (in shares) at Dec. 31, 2019			29,601,000
Beginning balance at Dec. 31, 2019	$ 852,401		$ 429,514	417,764		(2,587)	2,587	5,123
Ending balance (in shares) at Dec. 31, 2020	28,579,335		28,579,000
Ending balance at Dec. 31, 2020	$ 893,421	$ (17,051)	$ 400,582	478,489	$ (17,051)	(2,243)	2,243	14,350
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Accounting Standards Update [Extensible Enumeration]	us-gaap:AccountingStandardsUpdate201613Member
Net income	$ 28,194			28,194
Cash dividends declared	(5,688)			(5,688)
Change in Rabbi Trust obligation	0					(13)	13
Stock repurchases (in shares)			(107,000)
Stock repurchases	(4,036)		$ (4,036)
Stock withheld for payment of taxes (in shares)			(3,000)
Stock withheld for payment of taxes	(103)		$ (103)
Stock-based compensation (in shares)			20,000
Stock-based compensation	651		$ 651
Other comprehensive income (loss)	$ (18,535)							(18,535)
Ending balance (in shares) at Mar. 31, 2021	28,489,474		28,489,000
Ending balance at Mar. 31, 2021	$ 876,853		$ 397,094	$ 483,944		$ (2,256)	$ 2,256	$ (4,185)