Fair Value Measurements - Additional Information (Detail) (USD $)	3 Months Ended	12 Months Ended
	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Specific adjustments to impaired loans recognized	$ 37,000	$ 947,000
Transfers between level 1 and 2	0	0
Liabilities measured at fair value on a recurring or nonrecurring basis	0	0
Fair Value Measurements, Level 3 Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Amortized cost of Level 3 securities	119,750,000		33,951,000
Unrealized loss	$ 875,000		$ 870,000