Fair Value Measurement of Assets and Liabilities - Additional Information (Detail) (USD $)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014	Dec. 31, 2013
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Transfer of loans to loans held for sale	$ 0	$ 27,329,000
Impaired collateral dependent loans, charge-offs	850,000	1,000,000
Collateral dependent impaired loans, recorded investment	11,900,000
Specific valuation allowance allocations	1,900,000
Reported net carrying amount of impaired loans	10,000,000
Valuation of loan servicing rights, discount rate	8.00%
Net recoveries of impairment charges	84,000	100,000
Fair Value, Unobservable Inputs Quantitative Information For Assets Measured On Nonrecurring Basis, Foreclosed Assets, Discount Rate	4.80%
Foreclosed assets measured at fair value upon initial recognition	2,400,000
Allowance for loan losses, charge-offs	500,000	1,500,000
Loss due to re-measurement of repossessed assets	1,800,000
Minimum [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Valuation of loan servicing rights, prepayment rate	0.00%
Maximum [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Valuation of loan servicing rights, prepayment rate	25.00%
Significant Unobservable Inputs (Level 3) [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Discount rate on impaired loans	38.20%
Non-Performing Loans [Member] | Fair Value [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Transfer of loans to loans held for sale	7,100,000
Available-for-sale Securities [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Changes in unrealized losses on Level 3 securities	0	0
Impaired trust preferred securities ,fair value	$ 15,468,000	$ 26,911,000	$ 19,309,000	$ 28,523,000