Accounting for Investments in Qualified Affordable Housing Projects - Additional Information (Detail) (USD $)	0 Months Ended	3 Months Ended		9 Months Ended		12 Months Ended
	Jan. 01, 2012	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013
Adjusted Earnings Before Interest Taxes Depreciation And Amortization And Other Non Cash Items [Abstract]
Cumulative effect of retrospective application of accounting principle	$ 1,100,000
Increased in net income			135,000		51,000
Impairment of investments				0		0
Investment in low income housing		21,800,000		21,800,000		3,000,000
Unfunded commitments on low income housing		12,600,000		12,600,000		0
Income tax expense		592,000		1,000,000
Tax credit and other benefit received from tax expenses		$ 821,000		$ 1,400,000