Summary of Significant Accounting Policies - Cash and Cash Equivalents (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	$ 212,473	$ 200,218	$ 184,620	$ 530,670	$ 377,205	$ 164,798
Cash equivalents	140,000		98,000
Domestic Bank Accounts
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	176,905		156,122
Foreign Bank Accounts
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	35,568		28,498
Domestic Joint Ventures
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	13,871		7,714
Foreign Joint Ventures
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	4,873		3,973
Investments in Joint Ventures
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	18,744		11,687
Captive Insurance Company
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	132,024		85,014
Cash Not Held by Joint Ventures
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	$ 61,705		$ 87,919