Summary of Long-Term Debt (Detail) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Credit facility 2	[1]	$ 321,000	$ 77,000
Second Lien Facility		200,000	200,000
Unamortized Loan Commitment and Origination Fees and Unamortized Discounts or Premiums	[2]	9,625	11,733
Debt Instrument, Unamortized Discount	[2]	(3,159)	(3,839)
Unamortized Debt Issuance Expense	[2]	(6,466)	(7,894)
Long-term Debt		521,000	277,000
Debt Instrument, Unamortized Discount (Premium) and Debt Issuance Costs, Net		$ 511,375	$ 265,267
Second Lien Facility [Member]
Debt Instrument [Line Items]
Credit facility interest rate option one, applicable margin rate over Adjusted LIBOR		7.00%
Second Lien Facility, Interest Rate		9.53%

[1] 2 Issuance costs of the Credit Facility, which represent costs attributable to the access to credit over its contractual term, have been presented as a component of Other assets (see Note 13) and are being amortized over the term of the Credit Facility using the straight-line method.

[2] 1 Discount and issuance costs of the Second Lien Facility are being amortized over the term of the underlying loan using the effective-interest method.