CONSOLIDATED STATEMENT OF CHANGES IN SHAREHOLDERS' EQUITY - USD ($) $ in Thousands	Common Stock [Member]	Treasury Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Deficit [Member]	Accumulated Other Comprehensive Loss [Member]	Total
Balance at Dec. 31, 2016	$ 55,419	$ (866)	$ 360,564	$ (111,941)	$ (4,213)	$ 298,963
Balance (in shares) at Dec. 31, 2016	55,419,204
Net income				7,963		7,963
Common stock issuance expense			(200)			(200)
Common stock issued from restricted shares, net of tax benefits	$ 339		(338)			1
Common stock issued from restricted shares, net of tax benefits (in shares)	338,355
Stock-based compensation			775			775
Other comprehensive loss net of reclassification adjustments and tax					2,267	2,267
Balance at Mar. 31, 2017	$ 55,758	(866)	360,801	(103,978)	(1,946)	309,769
Balance (in shares) at Mar. 31, 2017	55,757,559
Balance at Dec. 31, 2016	$ 55,419	(866)	360,564	(111,941)	(4,213)	298,963
Balance (in shares) at Dec. 31, 2016	55,419,204
Net income						34,108
Other comprehensive loss net of reclassification adjustments and tax						4,190
Balance at Sep. 30, 2017	$ 55,860	(866)	362,340	(77,850)	(23)	339,461
Balance (in shares) at Sep. 30, 2017	55,859,660
Balance at Mar. 31, 2017	$ 55,758	(866)	360,801	(103,978)	(1,946)	309,769
Balance (in shares) at Mar. 31, 2017	55,757,559
Net income				18,864		18,864
Common stock issued from restricted shares, net of tax benefits	$ 100		(101)			(1)
Common stock issued from restricted shares, net of tax benefits (in shares)	100,086
Stock-based compensation			778			778
Other comprehensive loss net of reclassification adjustments and tax					1,609	1,609
Balance at Jun. 30, 2017	$ 55,858	(866)	361,478	(85,114)	(337)	331,019
Balance (in shares) at Jun. 30, 2017	55,857,645
Net income				7,281		7,281
Common stock issued from restricted shares, net of tax benefits	$ 2		15	(17)
Common stock issued from restricted shares, net of tax benefits (in shares)	2,015
Stock-based compensation			847			847
Other comprehensive loss net of reclassification adjustments and tax					314	314
Balance at Sep. 30, 2017	$ 55,860	(866)	362,340	(77,850)	(23)	339,461
Balance (in shares) at Sep. 30, 2017	55,859,660
Balance at Dec. 31, 2017	$ 55,861	(866)	363,196	(89,485)	(4,557)	$ 324,149
Balance (in shares) at Dec. 31, 2017	55,861,150					55,861,150
Net income				14,140		$ 14,140
Common stock issued from option exercises, net of tax benefits	$ 13		107	(9)		111
Common stock issued from option exercises, net of tax benefits (in shares)	13,390
Common stock issued from restricted shares, net of tax benefits	$ 433		(433)
Common stock issued from restricted shares, net of tax benefits (in shares)	433,344
Stock-based compensation			743			743
Other comprehensive loss net of reclassification adjustments and tax					(9,252)	(9,252)
Balance at Mar. 31, 2018	$ 56,307	(866)	363,613	(75,354)	(13,809)	329,891
Balance (in shares) at Mar. 31, 2018	56,307,884
Balance at Dec. 31, 2017	$ 55,861	(866)	363,196	(89,485)	(4,557)	$ 324,149
Balance (in shares) at Dec. 31, 2017	55,861,150					55,861,150
Net income						$ 81,558
Other comprehensive loss net of reclassification adjustments and tax						(16,962)
Balance at Sep. 30, 2018	$ 56,446	(866)	365,749	(7,936)	(21,519)	$ 391,874
Balance (in shares) at Sep. 30, 2018	56,446,088					56,446,088
Balance at Mar. 31, 2018	$ 56,307	(866)	363,613	(75,354)	(13,809)	$ 329,891
Balance (in shares) at Mar. 31, 2018	56,307,884
Net income				6,141		6,141
Common stock issued from restricted shares, net of tax benefits	$ 104		(103)			1
Common stock issued from restricted shares, net of tax benefits (in shares)	102,641
Stock-based compensation			950			950
Other comprehensive loss net of reclassification adjustments and tax					(4,436)	(4,436)
Balance at Jun. 30, 2018	$ 56,411	(866)	364,460	(69,213)	(18,245)	332,547
Balance (in shares) at Jun. 30, 2018	56,410,525
Net income				61,277		61,277
Common stock issued from restricted shares, net of tax benefits	$ 35		(35)
Common stock issued from restricted shares, net of tax benefits (in shares)	35,563
Stock-based compensation			1,324			1,324
Other comprehensive loss net of reclassification adjustments and tax					(3,274)	(3,274)
Balance at Sep. 30, 2018	$ 56,446	$ (866)	$ 365,749	$ (7,936)	$ (21,519)	$ 391,874
Balance (in shares) at Sep. 30, 2018	56,446,088					56,446,088