Goodwill and Intangible Assets - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Goodwill [Line Items]
Goodwill and intangible assets with indefinite lives	$ 63,059	$ 63,443
Amortization expense associated with identifiable intangible assets	400	700	$ 2,300
Estimated total amortization expense 2018	400
Estimated total amortization expense 2019	400
Estimated total amortization expense 2020	400
Estimated total amortization expense 2021	400
Estimated total amortization expense 2022	400
Indefinite-lived Intangible Assets [Member]
Goodwill [Line Items]
Goodwill and intangible assets with indefinite lives	$ 59,700	$ 59,700