Fair Value Measurements - Assets and Liabilities Measured at Fair Value on Nonrecurring Basis (Detail) - USD ($)	Sep. 30, 2015	Dec. 31, 2014	Sep. 30, 2014
ASSETS MEASURED ON A NONRECURRING BASIS
Loans held for sale	$ 0	$ 0	$ 0
Nonrecurring [Member]
ASSETS MEASURED ON A NONRECURRING BASIS
Impaired loans	3,000,000	5,000,000	6,000,000
Loans held for sale	0	0	0
Accrued income and other assets	6,000,000	7,000,000	4,000,000
Total assets at fair value	9,000,000	12,000,000	10,000,000
Level 1 [Member] | Nonrecurring [Member]
ASSETS MEASURED ON A NONRECURRING BASIS
Loans held for sale	0	0	0
Level 2 [Member] | Nonrecurring [Member]
ASSETS MEASURED ON A NONRECURRING BASIS
Loans held for sale	0	0	0
Level 3 [Member] | Nonrecurring [Member]
ASSETS MEASURED ON A NONRECURRING BASIS
Impaired loans	3,000,000	5,000,000	6,000,000
Loans held for sale	0	0	0
Accrued income and other assets	6,000,000	7,000,000	4,000,000
Total assets at fair value	$ 9,000,000	$ 12,000,000	$ 10,000,000