Share Capital - Additional Information (Narrative) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019	Jul. 26, 2019	Jun. 30, 2019	Dec. 31, 2018
Class of Stock [Line Items]
Amounts pledged	$ 150,547		$ 357,120
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	12,610,740	12,923,517	12,698,703	12,756,308		12,941,809
Common Stock, Shares, Issued	12,610,740		12,698,703
Repurchase and cancelled stock	409,504	79,383
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]
Stock Repurchase Program, Remaining Number of Shares Authorized to be Repurchased					26,192
New Program [Member] | Class A Stock
Class of Stock [Line Items]
Repurchase of class A common stock				640,000
Stock Repurchase Program Percentage Of Shares Repurchase Of Outstanding Share				5.00%
Stock Repurchase Program, Remaining Number of Shares Authorized to be Repurchased	180,031			666,192
Repurchase and cancelled stock	409,504	79,383
Treasury Stock, Retired, Cost Method, Amount	$ 8,400	$ 2,000
Treasury Stock Acquired, Average Cost Per Share	$ 20.60	$ 25.64