Goodwill and Intangible Assets - Additional Information (Detail) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Goodwill [Line Items]
Goodwill and intangible assets with indefinite lives	$ 63,155		$ 63,443
Amortization expense associated with identifiable intangible assets	300	$ 600
Estimated total amortization expense 2017	400
Estimated total amortization expense 2018	400
Estimated total amortization expense 2019	400
Estimated total amortization expense 2020	400
Estimated total amortization expense 2021	400
Indefinite-lived Intangible Assets [Member]
Goodwill [Line Items]
Goodwill and intangible assets with indefinite lives	$ 59,700		$ 59,700