Goodwill and Intangible Assets - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Goodwill And Intangible Assets Disclosure [Abstract]
Amortization expense	$ 2,400	$ 2,400	$ 7,296	$ 7,139
Estimated amortization expense, remainder of 2018	2,400		2,400
Estimated amortization expense, year 2019	9,600		9,600
Estimated amortization expense, year 2020	9,600		9,600
Estimated amortization expense, year 2021	9,600		9,600
Estimated amortization expense, year 2022	9,600		9,600
Estimated amortization expense, thereafter	$ 54,000		$ 54,000