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	$ 31,913
Common stock issued upon exercise of options, Shares	0
Ending Balance at Jun. 30, 2017						2,416
Beginning Balance at Mar. 31, 2017						460
Comprehensive income	$ 17,437
Ending Balance at Jun. 30, 2017						2,416
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	$ 27,430				33,125	(5,695)
Impact of adoption of ASU | ASU 2016-01 [Member]	614				614
Impact of adoption of ASU | ASU 2018-02 [Member]	(414)				(414)
Common stock issued upon exercise of options	$ 67		67
Common stock issued upon exercise of options, Shares	15,000	15,000
Common stock issued	$ 196	$ 1	195
Common stock issued, Shares		9,065
Share-based compensation	552		552
Dividends to shareholders	(8,477)				(8,477)
Ending Balance at Jun. 30, 2018	$ 445,391	$ 205	210,895	$ (22,370)	258,744	(2,083)
Ending Balance, Shares at Jun. 30, 2018	20,528,230	20,528,230
Treasury Stock Ending Balance, Shares at Jun. 30, 2018	(1,258,250)			(1,258,250)
Beginning Balance at Mar. 31, 2018						(2,236)
Comprehensive income	$ 17,109
Ending Balance at Jun. 30, 2018	$ 445,391	$ 205	$ 210,895	$ (22,370)	$ 258,744	$ (2,083)
Ending Balance, Shares at Jun. 30, 2018	20,528,230	20,528,230
Treasury Stock Ending Balance, Shares at Jun. 30, 2018	(1,258,250)			(1,258,250)