Recently Issued Accounting Pronouncements - Additional Information (Detail) - USD ($)	9 Months Ended		12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Investments held in Qualified Affordable Housing Projects	$ 40,579,000		$ 32,778,000
Tax credits and other tax benefits recognized	6,672,000	$ 5,817,000
Amortized cost of investments	$ 5,834,000	$ 4,033,000
Qualified Affordable Housing Project [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Investment in unconsolidated affiliates asset			(7,504,000)
Deferred tax liability			(2,937,000)
Reduction in the opening balance of stockholders' equity			$ (4,567,000)