Share Capital - Narrative (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Jun. 30, 2017	May 05, 2017	Dec. 31, 2016	Jun. 30, 2016	Dec. 31, 2015	Sep. 15, 2015
Class of Stock [Line Items]
Preferred stock, authorized (in shares)	50,000,000		50,000,000
Preferred stock, par value (dollars per share)	$ 0.001		$ 0.001
Preferred stock, issued (in shares)	0		0
Class A Stock [Member]
Class of Stock [Line Items]
Common stock, shares authorized (in shares)	50,000,000		50,000,000				50,000,000
Common stock, par value (dollars per share)	$ 0.001		$ 0.001				$ 0.001
Common stock, shares issued (in shares)	13,009,648		13,009,648				13,261,095
Common stock, shares outstanding (in shares)	13,009,648	13,268,439	13,009,648	13,268,439	13,132,775		13,261,095	13,259,715	13,238,486
Repurchased and canceled pursuant to the stock buy-back (in shares)	143,010	2,264	450,350	253,518
Class A Stock [Member] | New Program [Member]
Class of Stock [Line Items]
Common stock, shares issued (in shares)						13,178,571
Common stock, shares outstanding (in shares)						13,178,571
Number of shares authorized to be repurchased (in shares)						650,000
Stock Repurchase Program Percentage Of Shares Repurchase Of Outstanding Share						5.00%
Repurchased and canceled pursuant to the stock buy-back (in shares)	143,010		450,350
Stock repurchased and retired during period, value	$ 2.3		$ 7.5
Stock repurchased and retired during period (dollars per share)	$ 16.12		$ 16.57
Remaining number of shares authorized to be repurchased (in shares)	508,906		508,906			690,734
Class A Stock [Member] | Previous Program [Member]
Class of Stock [Line Items]
Number of shares authorized to be repurchased (in shares)										665,000
Remaining number of shares authorized to be repurchased (in shares)										40,734
Class B Stock [Member]
Class of Stock [Line Items]
Common stock, shares authorized (in shares)	99,665		99,665				99,665
Common stock, par value (dollars per share)	$ 0.001		$ 0.001				$ 0.001
Common stock, shares issued (in shares)	99,665		99,665				99,665
Common stock, shares outstanding (in shares)	99,665		99,665				99,665