Income Taxes - Carryforwards Expiration (Detail) $ in Thousands	Dec. 31, 2017 USD ($)
Income Tax Disclosure [Abstract]
2018	$ 0
2019	0
2020	0
2021	3,728
2022 and thereafter	250,572
Total	$ 254,300

Amount of operating loss carryforward, before tax effects, available to reduce future taxable income under enacted tax laws.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32559-109319

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