Investments in Limited Partnerships - Additional Information (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2016 USD ($) Partnership	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Schedule of Investments [Line Items]
Amount invested in partnerships	$ 14,300	$ 3,100
Unfunded equity commitments in other liabilities	8,200	2,100
Income (loss) from equity method investments	900	600	$ 900
Tax benefits including low-income housing and historic tax credits	$ 800	500	700
Number of limited partnerships held | Partnership	7
Investment in partnership recorded in other assets	$ 5,200	5,200
Partnership gains (losses) under equity method	19	(1)	$ 300
AMSCO Inc [Member]
Schedule of Investments [Line Items]
Income (loss) from equity method investments	500	300
Equity method investment	$ 8,300	$ 7,700