Income Taxes - Schedule of Non-Current Deferred Tax Assets and Liabilities Balance Sheet Captions (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Other assets	$ 117	$ 95
Deferred income taxes	$ 83,571	$ 54,995

Amount, after deferred tax asset, of deferred tax liability attributable to taxable differences with jurisdictional netting.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32537-109319

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 45
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=84176650&loc=d3e31931-109318

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant