Revenue from Contracts with Customers - Impact to Financial Statements Affected by Adoption of Topic 606 (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Equipment held for sale	$ 789				$ 34,172				$ 789	$ 34,172
Spare parts inventory	48,874				16,379				48,874	16,379
Revenue:
Spare parts and equipment sales									71,141	51,423	$ 17,783
Gain on sale of leased equipment									6,944	4,929	3,482
Expenses:
Cost of spare parts and equipment sales									61,025	40,848	13,293
Net income									43,231	62,158	14,069
Net income attributable to common shareholders	17,274	$ 8,834	$ 7,528	$ 6,261	$ 41,864	$ 4,939	$ 5,657	$ 7,839	39,898	$ 60,299	$ 13,780
Increase in cash flows from operating activities									16,900
Decrease in proceeds from sale of equipment									16,900
ASU 2014-09 | Balance without adoption of ASC Topic 606
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Equipment held for sale	23,733								23,733
Spare parts inventory	25,930								25,930
Revenue:
Spare parts and equipment sales									54,749
Gain on sale of leased equipment									7,644
Expenses:
Cost of spare parts and equipment sales									45,333
Net income									43,231
Net income attributable to common shareholders									39,898
ASU 2014-09 | Impact of adoption
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Equipment held for sale	(22,944)								(22,944)
Spare parts inventory	$ 22,944								22,944
Revenue:
Spare parts and equipment sales									16,392
Gain on sale of leased equipment									(700)
Expenses:
Cost of spare parts and equipment sales									$ 15,692