Goodwill and Other Intangible Assets - Additional Information (Detail) - USD ($)		12 Months Ended
	Jan. 01, 2015	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Goodwill And Other Intangible Assets [Line Items]
Amortization of Intangible Assets		$ 3,600,000	$ 3,300,000	$ 2,300,000
Goodwill		112,657,000	67,717,000	57,517,000
Additional goodwill		44,940,000	10,200,000
Goodwill impairment		0	0	0
Material impairments to identifiable intangible assets		0	0	0
Aggregate fair value of mortgage servicing rights		$ 8,000,000	$ 6,900,000
Range of discount rates used for valuation of mortgage servicing rights		10.00%	10.00%
Valley Green Bank [Member]
Goodwill And Other Intangible Assets [Line Items]
Additional goodwill	$ 43,500,000
Customer Related Intangibles [Member]
Goodwill And Other Intangible Assets [Line Items]
Impairment on customer related intangibles		$ 0	$ 31,000	$ 83,000
Core Deposits [Member] | Valley Green Bank [Member]
Goodwill And Other Intangible Assets [Line Items]
Core deposit intangibles	$ 1,500,000