Condensed Consolidated Statement of Changes in Shareholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Common Stock [Member]	Treasury Stock [Member]	Additional Paid-In Capital [Member]	Accumulated Earnings [Member]	Accumulated Other Comprehensive Income [Member]
Beginning Balance at Dec. 31, 2014						$ 2,810
Comprehensive income	$ 47,939
Common stock issued upon exercise of options, Shares	156,850
Ending Balance at Sep. 30, 2015						3,360
Beginning Balance at Jun. 30, 2015						2,052
Comprehensive income	$ 19,248
Ending Balance at Sep. 30, 2015						3,360
Beginning Balance at Dec. 31, 2015	$ 453,981	$ 203	$ (22,370)	$ 204,688	$ 268,873	2,587
Beginning Balance, Shares at Dec. 31, 2015	20,388,396	20,388,396
Treasury Stock Beginning Balance, Shares at Dec. 31, 2015	(1,258,250)		(1,258,250)
Comprehensive income	$ 62,801				58,792	4,009
Common stock issued upon exercise of options	$ 837	$ 1		836
Common stock issued upon exercise of options, Shares	68,879	68,879
Tax benefit from share-based payments	$ 976			976
Restricted common stock issued	603			603
Restricted common stock issued, Shares		31,110
Share-based compensation	906			906
Dividends to shareholders	(10,361)				(10,361)
Ending Balance at Sep. 30, 2016	$ 509,743	$ 204	$ (22,370)	208,009	317,304	6,596
Ending Balance, Shares at Sep. 30, 2016	20,488,385	20,488,385
Treasury Stock Ending Balance, Shares at Sep. 30, 2016	(1,258,250)		(1,258,250)
Beginning Balance at Jun. 30, 2016						8,309
Comprehensive income	$ 16,183
Ending Balance at Sep. 30, 2016	$ 509,743	$ 204	$ (22,370)	$ 208,009	$ 317,304	$ 6,596
Ending Balance, Shares at Sep. 30, 2016	20,488,385	20,488,385
Treasury Stock Ending Balance, Shares at Sep. 30, 2016	(1,258,250)		(1,258,250)