Fair Value Measurements - Additional Information about Assets Measured at Fair Value on Recurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance at beginning of period	$ 33,749	$ 32,565
Total gains (losses) - realized/unrealized, Included in earnings	13,766	78
Total gains (losses) - realized/unrealized, Included in other comprehensive income	5,676	6,705
Accretion included in earnings	662	3,176
Purchases	0	0
Issuances		38
Sales/redemptions	(51,527)	(1,033)
Settlements	(431)	(1,698)
Transfers from Level 3		(6,082)
Transfers into Level 3	0	0
Balance at end of period	1,895	33,749
Pooled Trust Preferred Collateralized Debt Obligations [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance at beginning of period	31,595	22,456
Total gains (losses) - realized/unrealized, Included in earnings	13,766
Total gains (losses) - realized/unrealized, Included in other comprehensive income	5,608	6,701
Accretion included in earnings	657	3,160
Purchases	0	0
Issuances		38
Sales/redemptions	(51,527)
Settlements	(99)	(760)
Transfers into Level 3	0	0
Balance at end of period		31,595
Other Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance at beginning of period		6,892
Total gains (losses) - realized/unrealized, Included in earnings		78
Total gains (losses) - realized/unrealized, Included in other comprehensive income		21
Accretion included in earnings		4
Purchases	0	0
Sales/redemptions		(1,033)
Transfers from Level 3		(5,962)
Transfers into Level 3	0	0
Equity Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance at beginning of period	410	512
Total gains (losses) - realized/unrealized, Included in other comprehensive income	65	18
Purchases	0	0
Transfers from Level 3		(120)
Transfers into Level 3	0	0
Balance at end of period	475	410
Residential Non-Agency Collateralized Mortgage Obligations [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance at beginning of period	1,744	2,705
Total gains (losses) - realized/unrealized, Included in other comprehensive income	3	(35)
Accretion included in earnings	5	12
Purchases	0	0
Settlements	(332)	(938)
Transfers into Level 3	0	0
Balance at end of period	$ 1,420	$ 1,744