Investment Securities - Additional Information (Detail) (USD $)	6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Trading securities	$ 0
Held-to-maturity securities	0
Securities pledged as collateral	504,700,000
FHLB pledged investment securities	11,000,000
Proceeds from sale of investment securities	140,900,000	220,300,000
Net gains from sale of investment securities	943,000	2,500,000
Losses from sale of investment securities	0
Unamortized premiums	23,100,000
Unaccreted discounts	220,000
Owned investment securities	525,244,000		747,718,000
Total unrealized losses on securities	8,666,000		34,754,000
Mortgage-Backed Securities ("MBS") [Member]
Schedule of Available-for-sale Securities [Line Items]
Weighted average duration of MBS portfolio	5 years 2 months 12 days
OTTI on evaluation of securities	$ 0