Share Capital - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								9 Months Ended	12 Months Ended			39 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Sep. 30, 2015	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2014	Sep. 15, 2015	Oct. 07, 2011
Class of Stock [Line Items]
Preferred stock, authorized (in shares)	50,000,000									50,000,000
Preferred stock, par value (in dollars per share)	$ 0.001									$ 0.001
Preferred stock, issued (in shares)	0									0
Dividends per share (in dollars 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 (in shares)	50,000,000				50,000,000					50,000,000	50,000,000		50,000,000
Common stock, par value (in dollars per share)	$ 0.001				$ 0.001					$ 0.001	$ 0.001		$ 0.001
Common stock, outstanding (in shares)	13,238,486				13,530,688					13,238,486	13,530,688	13,377,967	13,530,688
Common stock, issued (in shares)	13,238,486				13,530,688					13,238,486	13,530,688		13,530,688
Dividends per share (in dollars per share)										$ 0.44	$ 0.44	$ 0.44
Class A Stock | New Program
Class of Stock [Line Items]
Common stock, outstanding (in shares)														13,348,369
Repurchase of class A common stock (in shares)														665,000
Percentage of repurchase of class A common stock														5.00%
Common stock, issued (in shares)														13,348,369
Stock repurchased and retired during period (in shares)	94,882
Stock repurchased and retired during period, value	$ 1.6
Stock repurchased and retired during period (in dollars per share)	$ 17.20
Remaining number of shares authorized to be repurchased (in shares)	570,118									570,118
Class A Stock | Previous Program
Class of Stock [Line Items]
Repurchase of class A common stock (in shares)															675,000
Stock repurchased and retired during period (in shares)									328,844				322,177
Stock repurchased and retired during period, value									$ 6.6
Stock repurchased and retired during period (in dollars per share)									$ 20.12
Remaining number of shares authorized to be repurchased (in shares)		23,979							23,979
Class B Stock
Class of Stock [Line Items]
Common stock, authorized (in shares)	99,680				99,680					99,680	99,680		99,680
Common stock, par value (in dollars per share)	$ 0.001				$ 0.001					$ 0.001	$ 0.001		$ 0.001
Common stock, outstanding (in shares)	99,680				99,680					99,680	99,680		99,680
Common stock, issued (in shares)	99,680				99,680					99,680	99,680		99,680
Dividends per share (in dollars per share)										$ 0.44	$ 0.44	$ 0.44