Interes Rates on Senior Secured Credit Facilities (Detail) - Senior Secured Credit Facilities	12 Months Ended
	Dec. 31, 2017
Term Loan A
Debt Instrument [Line Items]
Debt instrument, interest rate at period end	3.32%
Term Loan A-1 Facility
Debt Instrument [Line Items]
Debt instrument, interest rate at period end	3.32%
Term Loan B3 Facility
Debt Instrument [Line Items]
Debt instrument, interest rate at period end	3.82%
LIBOR | Term Loan A
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate	1.75%
LIBOR | Term Loan A-1 Facility
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate	1.75%
LIBOR | Term Loan B3 Facility
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate	2.25%
LIBOR | Revolving Facility
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate	1.75%	[1]

[1] Includes unused commitment fee of 0.30% and letter of credit fee of 1.75% not reflected in interest rate above.