Other Assets and Accrued Liabilities - Asset Removal Obligations (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance at beginning of year	$ 29,166	$ 21,703	$ 21,507
Additional liabilities accrued	2,741	3,357	2,404
Changes to prior estimates	3,902	3,504	(1,695)
Payments	(224)	(443)	(1,296)
Accretion expense	1,477	1,045	783
Balance at end of year	$ 37,062	$ 29,166	$ 21,703