Financial Instruments and Fair Value Measurements - Carrying Value and Estimated Fair Values (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Financial assets
Interest rate swap	$ 2,304	$ 214
Carrying Amount
Financial assets
Interest rate swap	2,304	214
Carrying Amount | Credit Facility | Senior Secured Term B Loan
Financial liabilities
Senior secured term loan	375,563	376,395
Carrying Amount | Credit Facility | 2018 Term A Loan
Financial liabilities
Senior secured term loan	0	26,690
Carrying Amount | Credit Facility | 2020 Term A Loan
Financial liabilities
Senior secured term loan	193,808	200,653
Fair Value
Financial assets
Interest rate swap	2,304	214
Fair Value | Credit Facility | Senior Secured Term B Loan
Financial liabilities
Senior secured term loan	378,100	370,540
Fair Value | Credit Facility | 2018 Term A Loan
Financial liabilities
Senior secured term loan	0	26,027
Fair Value | Credit Facility | 2020 Term A Loan
Financial liabilities
Senior secured term loan	$ 194,494	$ 196,584