Investment Securities - Additional Information (Detail) (USD $)	3 Months Ended		12 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Trading securities	$ 0
Securities pledged as collateral	423,900,000		470,400,000
FHLB pledged investment securities	0		0
Proceeds from sale of investment securities	37,400,000	37,800,000
Gains from sale of investment securities	451,000	578,000
Losses from sale of investment securities	0	0
Unamortized premiums	22,500,000		22,400,000
Unaccreted discounts	66,000		188,000
Held-to-maturity securities, unrealized loss			0
Owned investment securities	206,438,000		330,754,000
Total unrealized losses on securities	1,435,000		3,594,000
Mortgage-Backed Securities ("MBS") [Member]
Schedule of Available-for-sale Securities [Line Items]
Weighted average duration of MBS portfolio	3 years 9 months 18 days
OTTI on evaluation of securities	0		0
Bond [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair market value of investment			1,300,000
Municipal Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Number of securities transferred from available-for-sale to held-to-maturity			161
Securities transferred from available-for-sale to held-to-maturity, Fair value			$ 124,900,000