The Company (Detail)	6 Months Ended
	Jun. 30, 2018 USD ($) Segment	Jul. 23, 2018 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2014 USD ($)
Organization, Consolidation and Presentation of Financial Statements [Line Items]
Number of operating segments | Segment	1
Aggregate amount of senior notes issued	$ 125,000,000		$ 125,000,000
2014 Notes | 2014 Convertible Notes
Organization, Consolidation and Presentation of Financial Statements [Line Items]
Aggregate amount of senior notes issued	$ 125,000,000		$ 125,000,000.0	$ 125,000,000
Subsequent Event | Revolving Credit Facility | Delayed Draw Term Loan
Organization, Consolidation and Presentation of Financial Statements [Line Items]
Maximum borrowing capacity		$ 100,000,000