Goodwill and Intangible Assets - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Goodwill [Line Items]
Goodwill and intangible assets with indefinite lives	$ 62,963		$ 63,059
Amortization expense associated with identifiable intangible assets	100	$ 100
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