Summary of Significant Accounting Policies - Prior Period Adjustments (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Spare parts and equipment sales	$ 24,409	$ 11,529	$ 56,497	$ 36,168
Gain (loss) on sale of leased equipment	4,589	1,065	19,279	1,662
Cost of spare parts and equipment sales	$ 20,195	8,832	47,192	30,524
Cash flows provided by operating activities			170,817	115,528
Cash flows provided by financing activities			(89,204)	285,712
Impacts from ASC 606
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Spare parts and equipment sales		3,200		14,500
Gain (loss) on sale of leased equipment		(200)		(500)
Cost of spare parts and equipment sales		$ 3,000		14,000
Cash flows provided by operating activities				$ 14,700
Cash flows provided by financing activities			$ (14,700)

The aggregate cost of goods produced and sold and services rendered during the reporting period.

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