Amount of cash and cash equivalents restricted as to withdrawal or usage, classified as noncurrent. 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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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Organization and Significant Accounting Policies - Additional Information (Detail) - USD ($)	Jun. 30, 2018	Jan. 01, 2018	Dec. 31, 2017	Jun. 30, 2017
Organization And Summary Of Significant Accounting Policies [Line Items]
Restricted cash	$ 5,477,000		$ 4,500,000
Topic 606
Organization And Summary Of Significant Accounting Policies [Line Items]
Adjustment to retained earnings		$ 0
ASU 2016-18
Organization And Summary Of Significant Accounting Policies [Line Items]
Restricted cash	$ 5,500,000			$ 4,600,000