Share Capital - Additional Information (Narrative) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	May 15, 2020	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2018
Class of Stock [Line Items]
Amounts pledged	$ 357,323		$ 357,323				$ 357,120
Preferred stock, authorized	50,000,000		50,000,000
Preferred stock, par value	$ 0.001		$ 0.001
Preferred stock, issued	0		0
Class A Stock
Class of Stock [Line Items]
Common stock, authorized	50,000,000		50,000,000				50,000,000
Common stock, par value	$ 0.001		$ 0.001				$ 0.001
Common Stock, outstanding	12,445,479	12,756,308	12,445,479	12,756,308	12,636,523	12,610,740	12,698,703	12,923,517	12,941,809
Common Stock, Shares, Issued	12,445,479		12,445,479				12,698,703
Repurchase and cancelled stock	191,044	167,209	600,548	246,592
Class B Stock
Class of Stock [Line Items]
Common stock, authorized	99,665		99,665				99,665
Common stock, par value	$ 0.001		$ 0.001				$ 0.001
Common Stock, outstanding	99,665		99,665				99,665
Common Stock, Shares, Issued	99,665		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					98,625
New Program [Member] | Class A Stock
Class of Stock [Line Items]
Repurchase of class A common stock					530,000
Stock Repurchase Program Percentage Of Shares Repurchase Of Outstanding Share					4.20%
Stock Repurchase Program, Remaining Number of Shares Authorized to be Repurchased	518,987		518,987		628,625
Repurchase and cancelled stock	191,044		600,548
Treasury Stock, Retired, Cost Method, Amount	$ 3,800		$ 12,300
Treasury Stock Acquired, Average Cost Per Share	$ 20.06		$ 20.42