Consolidated Statements of Changes in Stockholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative Effect of New Accounting Principle in Period of Adoption | Accounting Standards Update 2016-01 [Member]	$ 0			$ 6,490	$ (6,490)
Balance, shares at Dec. 31, 2017	21,036,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation (shares)	36,000
Balance, shares at Mar. 31, 2018	21,072,000
Balance at Dec. 31, 2017	$ 238,189	$ 210	$ 155,082	73,502	9,395
Balance (Accounting Standards Update 2016-01 [Member]) at Dec. 31, 2017				79,992	2,905
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Reclassification of tax effects resulting from the TCJA	0
Reclassification of tax effects resulting from the TCJA | Accounting Standards Update 2018-02 [Member]				(1,308)	1,308
Issuance of stock under stock-based compensation plan	545	0	545
Stock-based compensation	158		158
Dividends declared	(1,473)			(1,473)
Other comprehensive income (loss)	(4,856)				(4,856)
Net income	7,287			7,287
Balance at Mar. 31, 2018	$ 239,850	210	155,785	84,498	(643)
Balance, shares at Dec. 31, 2017	21,036,000
Balance, shares at Jun. 30, 2018	21,169,000
Balance at Dec. 31, 2017	$ 238,189	210	155,082	73,502	9,395
Balance (Accounting Standards Update 2016-01 [Member]) at Dec. 31, 2017				79,992	2,905
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Other comprehensive income (loss)	(5,872)
Net income	17,399
Balance at Jun. 30, 2018	$ 247,945	211	156,264	93,129	(1,659)
Balance, shares at Mar. 31, 2018	21,072,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation (shares)	97,000
Balance, shares at Jun. 30, 2018	21,169,000
Balance at Mar. 31, 2018	$ 239,850	210	155,785	84,498	(643)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of stock under stock-based compensation plan	79	1	78
Stock-based compensation	401		401
Dividends declared	(1,481)			(1,481)
Other comprehensive income (loss)	(1,016)				(1,016)
Net income	10,112			10,112
Balance at Jun. 30, 2018	$ 247,945	211	156,264	93,129	(1,659)
Balance, shares at Dec. 31, 2018	21,241,504
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation (shares)	43,000
Balance, shares at Mar. 31, 2019	21,285,000
Balance at Dec. 31, 2018	$ 263,986	212	158,485	106,545	(1,256)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of stock under stock-based compensation plan	598	1	597
Stock-based compensation	507		507
Dividends declared	(1,702)			(1,702)
Other comprehensive income (loss)	6,780				6,780
Net income	18,720			18,720
Balance at Mar. 31, 2019	$ 288,889	213	159,589	123,563	5,524
Balance, shares at Dec. 31, 2018	21,241,504
Balance, shares at Jun. 30, 2019	21,356,399
Balance at Dec. 31, 2018	$ 263,986	212	158,485	106,545	(1,256)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Other comprehensive income (loss)	13,335
Net income	32,487
Balance at Jun. 30, 2019	$ 307,907	214	159,986	135,628	12,079
Balance, shares at Mar. 31, 2019	21,285,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares Withheld for Tax Withholding Obligation	(7,000)
Stock-based compensation (shares)	78,000
Balance, shares at Jun. 30, 2019	21,356,399
Balance at Mar. 31, 2019	$ 288,889	213	159,589	123,563	5,524
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of stock under stock-based compensation plan	394	1	393
Stock-based compensation	621		621
Restricted shares withheld for taxes	(617)		(617)
Dividends declared	(1,702)			1,702
Other comprehensive income (loss)	6,555
Net income	13,767			13,767
Balance at Jun. 30, 2019	$ 307,907	$ 214	$ 159,986	$ 135,628	$ 12,079