Condensed Consolidated Statement of Changes in Shareholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-In Capital [Member]	Treasury Stock [Member]	Accumulated Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]
Beginning Balance at Dec. 31, 2016						$ (492)
Comprehensive income	$ 14,476
Common stock issued upon exercise of options, Shares	0
Ending Balance at Mar. 31, 2017						460
Beginning Balance at Dec. 31, 2017	$ 425,423	$ 204	$ 210,081	$ (22,370)	$ 233,896	3,612
Beginning Balance, Shares at Dec. 31, 2017	20,504,165	20,504,165
Treasury Stock Beginning Balance, Shares at Dec. 31, 2017	(1,258,250)			(1,258,250)
Comprehensive income	$ 10,321				16,169	(5,848)
Impact of adoption of ASU | ASU 2016-01 [Member]	615				615
Impact of adoption of ASU | ASU 2018-02 [Member]	(414)				(414)
Common stock issued upon exercise of options	$ 68	$ 1	67
Common stock issued upon exercise of options, Shares	15,000	15,000
Share-based compensation	$ 293		293
Dividends to shareholders	(4,238)				(4,238)
Ending Balance at Mar. 31, 2018	$ 432,068	$ 205	$ 210,441	$ (22,370)	$ 246,028	$ (2,236)
Ending Balance, Shares at Mar. 31, 2018	20,519,165	20,519,165
Treasury Stock Ending Balance, Shares at Mar. 31, 2018	(1,258,250)			(1,258,250)