Goodwill and Intangible Assets - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Intangible Assets And Goodwill [Line Items]
Goodwill	$ 6,521,000	$ 6,521,000	$ 4,820,000
Impairment of goodwill	0	0
Amortization of definite lived intangible assets	500,000	500,000	400,000
Amortization of the value of business acquired	0	25,500,000	$ 0
Indefinite lived intangible assets	19,000,000	19,000,000
Impairment of indefinite lived intangible assets	0	0
Definite lived intangible assets	4,100,000	4,600,000
Impairment of definite lived intangible assets	$ 0	0
VOBA		$ 25,500,000