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Summary of Significant Accounting Policies - Prior Period Adjustments (Details) - USD ($) $ in Thousands | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2019 | Jun. 30, 2018 | Jun. 30, 2019 | Jun. 30, 2018
Revenue, Initial Application Period Cumulative Effect Transition [Line Items] |  |  |  |
Spare parts and equipment sales | $ 14,586 | $ 11,653 | $ 32,088 | $ 24,639
Gain (loss) on sale of leased equipment | 5,120 | 52 | 14,690 | 597
Cost of spare parts and equipment sales | $ 12,585 | 10,305 | 26,997 | 21,692
Cash flows provided by operating activities |  |  | 91,541 | 81,977
Cash flows provided by financing activities |  |  | (60,909) | 133,208
Impacts from ASC 606 |  |  |  |
Revenue, Initial Application Period Cumulative Effect Transition [Line Items] |  |  |  |
Spare parts and equipment sales |  | 4,600 |  | 11,300
Gain (loss) on sale of leased equipment |  | (200) |  | (300)
Cost of spare parts and equipment sales |  | $ 4,400 |  | 11,000
Cash flows provided by operating activities |  |  |  | $ 9,300
Cash flows provided by financing activities |  |  | $ (9,300) |

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