Commitments and Contingencies - Non Income Business Tax Liability Activity (Detail) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Commitments and Contingencies [Roll Forward]
Balance, beginning of year	$ 94	$ 3,427
Adjustments to existing liabilities	1,516	(2,110)
Payments	(827)	(1,223)
Balance, end of year	$ 783	$ 94

Carrying value as of the balance sheet date of obligations incurred and payable for real and property taxes. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer).

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.20)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 720
-SubTopic 30
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6419918&loc=d3e35281-107843

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section 45
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=82887183&loc=d3e6935-107765

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant