Summary of Significant Accounting Policies - Foreign Currency (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Accounting Policies [Abstract]
(Gain) loss on foreign currency related to re-measurement of U.S. dollar denominated debt held in Canada	$ (9,344)	$ (22,307)	$ 37,724
(Gain) loss on other transactions	(2,839)	1,200	(1,470)
(Gain) loss on foreign currency	$ (12,183)	$ (21,107)	$ 36,254