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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
Jun. 30, 2018
Dec. 31, 2017
Jun. 30, 2017
Dec. 31, 2016
Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents [Abstract]        
Cash and cash equivalents $ 33,786 $ 59,835    
Restricted cash, included in restricted cash and investments 24,862 60,370 $ 95,200 $ 290,600
Total cash, cash equivalents and restricted cash shown in the statement of cash flows $ 58,648 $ 120,205 $ 113,046 $ 341,330