Summary of Long-Term Debt (Detail) - USD ($)		Sep. 30, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity		$ 200,000,000
Revolving credit facility	[1]	57,000,000	$ 25,000,000
Second Lien Facility		200,000,000	0
Unamortized Loan Commitment and Origination Fees and Unamortized Discounts or Premiums		11,945,000	0
Debt Instrument, Unamortized Discount		(4,000,000)	0
Unamortized Debt Issuance Expense		(7,945,000)	0
Debt Instrument, Unamortized Discount (Premium) and Debt Issuance Costs, Net		245,055,000	25,000,000
Long-term Debt		257,000,000	$ 25,000,000
Revolving Credit Facility
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity		$ 237,500,000

[1] 2 Issuance costs of the Credit Facility, which represent costs attributable to the access to credit over it’s contractual term, have been presented as a component of Other assets (see Note 11) and are being amortized over the term of the Credit Facility using the straight-line method.