Summary of Operations and Significant Accounting Policies - Schedule of Reconciles of Cash, Cash Equivalents and Restricted Cash Balances (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents [Abstract]
Cash and cash equivalents	$ 44,570	$ 35,371	$ 59,835
Restricted cash, included in restricted cash and investments	228,771	105,331	60,370
Total cash, cash equivalents and restricted cash shown in the statement of cash flows	$ 273,341	$ 140,702	$ 120,205

Amount of cash and cash equivalents restricted as to withdrawal or usage. Cash includes, but is not limited to, currency on hand, demand deposits with banks or financial institutions, and other accounts with general characteristics of demand deposits. Cash equivalents include, but are not limited to, short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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Name:	us-gaap_RestrictedCashAndCashEquivalents
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant