Summary of Significant Accounting Policies - Cash and Cash Equivalents (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	$ 138,285	$ 112,183	$ 128,771	$ 190,515
Cash equivalents	7,100	8,800
Domestic Bank Accounts
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	83,100	19,500
Foreign Bank Accounts
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	55,200	92,700
Investments In Joint Ventures
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	16,700	11,500
Domestic Joint Ventures
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	$ 10,000	$ 10,000