Fair Value Measurements - Additional Information (Detail) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities at fair value	$ 0	$ 0	$ 0	$ 0	$ 0
Fair value of private placement bonds	18,800,000		18,800,000
Third party pricing for private placement bonds	18,800,000		18,800,000
Lower of the matrix price or par value of private placement bonds	18,800,000		18,800,000
Impaired financing receivable recorded investment reduction to estimated fair value	5,000,000		5,000,000
Estimated fair value of impaired loans and leases			12,800,000
Partial charge-offs to reduce carrying value of impaired loans and leases to estimated fair value	3,600,000		3,600,000
Specific loan and lease allocations to reduce carrying value of impaired loans and leases to estimated fair value			1,400,000
Partial charge-offs	400,000	1,100,000	1,700,000	1,300,000
Provision for loans and lease losses to cover charge-offs	$ 400,000	$ 1,100,000	1,700,000	$ 1,300,000
Impaired purchased loans			$ 12,300,000
Minimum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated cost to sell percentage			8.00%
Discount rate of other real estate			8.00%
Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated cost to sell percentage			10.00%
Discount rate of other real estate			9.50%