Share Capital - Additional Information (Narrative) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016	Dec. 31, 2015	Sep. 15, 2015	Oct. 07, 2011
Class of Stock [Line Items]
Amounts pledged	$ 705,988		$ 438,385
Preferred stock, authorized	50,000,000
Preferred stock, par value	$ 0.001
Preferred stock, issued	0
Class A Stock
Class of Stock [Line Items]
Common stock, authorized	50,000,000		50,000,000
Common stock, par value	$ 0.001		$ 0.001
Common Stock, outstanding	13,182,332	13,263,532	13,261,095	13,238,486	13,348,369
Common Stock, Shares, Issued	13,182,332		13,261,095
Repurchase and cancelled stock	257,783	240,274
Class B Stock
Class of Stock [Line Items]
Common stock, authorized	99,665		99,665
Common stock, par value	$ 0.001		$ 0.001
Common Stock, outstanding	99,665		99,665
Common Stock, Shares, Issued	99,665		99,665
Previous Program [Member] | Class A Stock
Class of Stock [Line Items]
Repurchase of class A common stock						675,000
New Program [Member] | Class A Stock
Class of Stock [Line Items]
Repurchase of class A common stock					665,000
Stock Repurchase Program Percentage Of Shares Repurchase Of Outstanding Share					5.00%
Stock Repurchased and Retired During Period, Shares	257,783
Stock Repurchased and Retired During Period, Value	$ 4,400
Stock Repurchased and Retired During Period, Per Share	$ 16.90
Stock Repurchase Program, Remaining Number of Shares Authorized to be Repurchased	51,473
Common Stock, Shares, Issued					13,348,369