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Acquisitions (Narrative) (Details) $ / shares in Units, shares in Millions |  | 2 Months Ended | 3 Months Ended | 6 Months Ended |
--- | --- | --- | --- | --- | ---
Feb. 17, 2017 USD ($) a $ / shares shares | Feb. 16, 2017 USD ($) | Jun. 30, 2017 USD ($) | Jun. 30, 2016 USD ($) | Jun. 30, 2017 USD ($) | Jun. 30, 2016 USD ($) | Dec. 15, 2016 $ / shares
Business Acquisition [Line Items] |  |  |  |  |  |  |
Acquisition expense |  |  | $ 1,060,000 | $ 0 | $ 2,358,000 | $ 0 |
Share price (in dollars per share) | $ / shares | $ 19.48 |  |  |  |  |  | $ 20.96
Vitruvian acquisition |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |
Net surface area | a | 46,400 |  |  |  |  |  |
Total consideration | $ 1,850,000,000 |  |  |  |  |  |
Payments to acquire businesses | $ 1,354,093,000 |  |  |  |  |  |
Equity interest issued or issuable, number of shares (in shares) | shares | 23.9 |  |  |  |  |  |
Acquisition expense |  |  | $ 1,100,000 |  | $ 2,400,000 |  |
Goodwill | $ 0 |  |  |  |  |  |
Bargain purchase gain | $ 0 |  |  |  |  |  |
Business acquisition, share price (in dollars per share) | $ / shares |  |  |  |  |  |  | $ 20.96
Decrease in fair value of shares issued for acquisition, amount |  | $ 35,300,000 |  |  |  |  |
Indemnity escrow | Vitruvian acquisition |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |
Equity interest issued or issuable, number of shares (in shares) | shares | 5.2 |  |  |  |  |  |

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