Share Capital - Additional Information (Narrative) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended			39 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2014	Sep. 15, 2015	Oct. 07, 2011
Class of Stock [Line Items]
Amounts pledged	$ 438,385				$ 546,334				$ 438,385	$ 546,334
Preferred stock, authorized	50,000,000								50,000,000
Preferred stock, par value	$ 0.001								$ 0.001
Preferred stock, issued	0								0
Dividends per share	$ 0.11	$ 0.11	$ 0.11	$ 0.11	$ 0.11	$ 0.11	$ 0.11	$ 0.11	$ 0.44	$ 0.44
Class A Stock
Class of Stock [Line Items]
Common stock, authorized	50,000,000				50,000,000				50,000,000	50,000,000
Common stock, par value	$ 0.001				$ 0.001				$ 0.001	$ 0.001
Common Stock, outstanding	13,261,095				13,238,486				13,261,095	13,238,486	13,530,688	13,530,688	13,348,369
Common Stock, Shares, Issued	13,261,095				13,238,486				13,261,095	13,238,486
Repurchase and cancelled stock									260,862	423,726
Dividends per share									$ 0.44	$ 0.44	$ 0.44
Class B Stock
Class of Stock [Line Items]
Common stock, authorized	99,665				99,680				99,665	99,680
Common stock, par value	$ 0.001				$ 0.001				$ 0.001	$ 0.001
Common Stock, outstanding	99,665				99,680				99,665	99,680
Common Stock, Shares, Issued	99,665				99,680				99,665	99,680
Dividends per share									$ 0.44	$ 0.44	$ 0.44
Previous Program [Member] | Class A Stock
Class of Stock [Line Items]
Repurchase of class A common stock														675,000
Stock Repurchased and Retired During Period, Shares										328,844		322,177
Stock Repurchased and Retired During Period, Value										$ 6,600
Stock Repurchased and Retired During Period, Per Share										$ 20.12
Stock Repurchase Program, Remaining Number of Shares Authorized to be Repurchased					23,979					23,979
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									260,862
Stock Repurchased and Retired During Period, Value									$ 3,900
Stock Repurchased and Retired During Period, Per Share									$ 15.09
Stock Repurchase Program, Remaining Number of Shares Authorized to be Repurchased	309,256								309,256
Common Stock, Shares, Issued													13,348,369