Summary of Significant Accounting Policies - Cash and Cash Equivalents (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2018
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	$ 377,205	$ 164,798	$ 85,423	$ 78,687
Cash equivalents	179,900	37,800
Domestic Bank Accounts
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	350,393	130,771
Foreign Bank Accounts
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	26,812	34,027
Domestic Joint Ventures
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	9,097	6,518
Foreign Joint Ventures
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	104	16
Investments in Joint Ventures
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	9,201	6,534
Cash Not Held by Joint Ventures
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	$ 368,004	$ 158,264