Interim Consolidated Statements of Shareholders' Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]
Beginning balance at Dec. 31, 2015	$ 465,275	$ 511	$ 222,328	$ 244,885	$ (2,449)
Common Stock, Shares, Outstanding, beginning balance at Dec. 31, 2015		22,076,534
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	28,156			28,156
Share-based compensation expense	827		827
Common stock issued	53,148	$ 0	53,148
Common stock issued, shares		2,744,815
Other comprehensive income	12,197				12,197
Ending balance at Jun. 30, 2016	559,603	$ 511	276,303	273,041	9,748
Common Stock, Shares, Outstanding, ending balance at Jun. 30, 2016		24,821,349
Beginning balance at Mar. 31, 2016					4,161
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	21,749
Other comprehensive income	5,587				5,587
Ending balance at Jun. 30, 2016	559,603	$ 511	276,303	273,041	9,748
Common Stock, Shares, Outstanding, ending balance at Jun. 30, 2016		24,821,349
Beginning balance at Dec. 31, 2016	$ 629,284	$ 511	336,149	303,036	(10,412)
Common Stock, Shares, Outstanding, beginning balance at Dec. 31, 2016	26,800,183	26,800,183
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	$ 20,192			20,192
Share-based compensation expense	1,211		1,211
Common stock issued	155	$ 0	155
Common stock issued, shares		74,688
Other comprehensive income	4,999				4,999
Ending balance at Jun. 30, 2017	$ 655,841	$ 511	337,515	323,228	(5,413)
Common Stock, Shares, Outstanding, ending balance at Jun. 30, 2017	26,874,871	26,874,871
Beginning balance at Mar. 31, 2017					(8,486)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	$ 11,209
Other comprehensive income	3,073				3,073
Ending balance at Jun. 30, 2017	$ 655,841	$ 511	$ 337,515	$ 323,228	$ (5,413)
Common Stock, Shares, Outstanding, ending balance at Jun. 30, 2017	26,874,871	26,874,871