Quarterly report pursuant to Section 13 or 15(d)

Basis of Presentation of Interim Period Statements - Schedule of Reconciles of Cash, Cash Equivalents and Restricted Cash Balances (Detail)

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Basis of Presentation of Interim Period Statements - Schedule of Reconciles of Cash, Cash Equivalents and Restricted Cash Balances (Detail) - USD ($)
$ in Thousands
Mar. 31, 2018
Dec. 31, 2017
Mar. 31, 2017
Dec. 31, 2016
Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents [Abstract]        
Cash and cash equivalents $ 24,000 $ 59,835    
Restricted cash, included in restricted cash and investments 30,788 60,370 $ 226,800 $ 290,600
Total cash, cash equivalents and restricted cash shown in the statement of cash flows $ 54,788 $ 120,205 $ 245,243 $ 341,330