Summary of Significant Accounting Policies - Goodwill (Details) - USD ($)	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Goodwill [Line Items]
Goodwill impairment	$ 0	$ 0	$ 9,100,000
Zentry Joint Venture
Goodwill [Line Items]
Goodwill impairment	$ 0	$ 0	$ 9,100,000

Amount of loss from the write-down of an asset representing the future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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