Basis of Presentation of Interim Period Statements - Schedule of Reconciles of Cash, Cash Equivalents and Restricted Cash Balances (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017
Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents [Abstract]
Cash and cash equivalents	$ 38,223	$ 35,371	$ 24,000	$ 59,835
Restricted cash, included in restricted cash and investments	158,333	105,331	30,788	60,370
Total cash, cash equivalents and restricted cash shown in the statement of cash flows	$ 196,556	$ 140,702	$ 54,788	$ 120,205