Share Capital - Additional Information (Narrative) (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Oct. 07, 2011
Class of Stock [Line Items]
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	$ 0.44000
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, issued	13,530,688				13,377,967				13,530,688	13,377,967		13,572,265
Common Stock, outstanding	13,530,688				13,377,967				13,530,688	13,377,967	13,508,318
Repurchase of class A common stock												675,000
Percentage of repurchase of class A common stock												5.00%
Repurchase and cancelled stock									0	200,578
Total consideration of repurchase and cancelled stock										$ 3.6
Repurchase and cancelled stock per share										$ 18.07
Dividends per share									$ 0.44	$ 0.44	$ 0.44
Class B Stock
Class of Stock [Line Items]
Common stock, authorized	99,680								99,680
Common stock, par value	$ 0.001				$ 0.001				$ 0.001	$ 0.001
Common stock, issued	99,680				99,680				99,680	99,680
Common Stock, outstanding	99,680				99,680				99,680	99,680
Dividends per share									$ 0.44	$ 0.44	$ 0.44