Summary of Significant Accounting Policies - Cash and Cash Equivalents (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	$ 164,798	$ 78,687	$ 138,285	$ 112,183
Cash equivalents	37,800	37,200
Held in Domestic Bank Accounts
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	130,771	62,495
Held in Foreign Bank Accounts
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	34,027	16,192
Held by Joint Ventures
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	6,534	8,985
Held by Domestic Joint Ventures
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	6,518	8,544
Held by Foreign Joint Ventures
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	16	441
Not Held by Joint Ventures
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	$ 158,264	$ 69,702