Impairment of Investment Securities - Pooled Trust Preferred Collateralized Debt Obligations (Detail) $ in Thousands	6 Months Ended
	Jun. 30, 2016 USD ($) Bank	Dec. 31, 2015 USD ($)
Impairment Of Investment Securities [Line Items]
Securities available for sale, at fair value	$ 855,333	$ 886,560
Unrealized Gain (Loss)	9,761	$ 16,477
Pooled Trust Preferred Collateralized Debt Obligations [Member]
Impairment Of Investment Securities [Line Items]
Book Value	42,750
Securities available for sale, at fair value	33,723
Unrealized Gain (Loss)	(9,027)
Pooled Trust Preferred Collateralized Debt Obligations [Member] | Mezzanine [Member] | Pre TSL IV [Member]
Impairment Of Investment Securities [Line Items]
Book Value	1,830
Securities available for sale, at fair value	1,301
Unrealized Gain (Loss)	$ (529)
Debt Instrument, Credit Rating	B1/BB
Number of Banks (in banks) | Bank	6
Deferrals and Defaults as a % of Current Collateral	18.05%
Excess Subordination as a % of Current Performing Collateral	58.51%
Pooled Trust Preferred Collateralized Debt Obligations [Member] | Mezzanine [Member] | Pre TSL VII [Member]
Impairment Of Investment Securities [Line Items]
Book Value	$ 3,061
Securities available for sale, at fair value	3,324
Unrealized Gain (Loss)	$ 263
Debt Instrument, Credit Rating	Ca/-
Number of Banks (in banks) | Bank	14
Deferrals and Defaults as a % of Current Collateral	49.68%
Excess Subordination as a % of Current Performing Collateral	0.00%
Pooled Trust Preferred Collateralized Debt Obligations [Member] | Mezzanine [Member] | Pre TSL VIII [Member]
Impairment Of Investment Securities [Line Items]
Book Value	$ 2,042
Securities available for sale, at fair value	1,691
Unrealized Gain (Loss)	$ (351)
Debt Instrument, Credit Rating	C/C
Number of Banks (in banks) | Bank	28
Deferrals and Defaults as a % of Current Collateral	53.00%
Excess Subordination as a % of Current Performing Collateral	0.00%
Pooled Trust Preferred Collateralized Debt Obligations [Member] | Mezzanine [Member] | Pre TSL IX [Member]
Impairment Of Investment Securities [Line Items]
Book Value	$ 2,394
Securities available for sale, at fair value	1,797
Unrealized Gain (Loss)	$ (597)
Debt Instrument, Credit Rating	B1/C
Number of Banks (in banks) | Bank	38
Deferrals and Defaults as a % of Current Collateral	29.80%
Excess Subordination as a % of Current Performing Collateral	9.73%
Pooled Trust Preferred Collateralized Debt Obligations [Member] | Mezzanine [Member] | Pre TSL X [Member]
Impairment Of Investment Securities [Line Items]
Book Value	$ 1,675
Securities available for sale, at fair value	1,817
Unrealized Gain (Loss)	$ 142
Debt Instrument, Credit Rating	Caa1/C
Number of Banks (in banks) | Bank	43
Deferrals and Defaults as a % of Current Collateral	32.22%
Excess Subordination as a % of Current Performing Collateral	2.20%
Pooled Trust Preferred Collateralized Debt Obligations [Member] | Mezzanine [Member] | Pre TSL XII [Member]
Impairment Of Investment Securities [Line Items]
Book Value	$ 5,786
Securities available for sale, at fair value	4,442
Unrealized Gain (Loss)	$ (1,344)
Debt Instrument, Credit Rating	B3/C
Number of Banks (in banks) | Bank	66
Deferrals and Defaults as a % of Current Collateral	22.03%
Excess Subordination as a % of Current Performing Collateral	0.00%
Pooled Trust Preferred Collateralized Debt Obligations [Member] | Mezzanine [Member] | Pre TSL XIII [Member]
Impairment Of Investment Securities [Line Items]
Book Value	$ 12,828
Securities available for sale, at fair value	9,971
Unrealized Gain (Loss)	$ (2,857)
Debt Instrument, Credit Rating	Ba3/C
Number of Banks (in banks) | Bank	56
Deferrals and Defaults as a % of Current Collateral	11.34%
Excess Subordination as a % of Current Performing Collateral	47.86%
Pooled Trust Preferred Collateralized Debt Obligations [Member] | Mezzanine [Member] | Pre TSL XIV [Member]
Impairment Of Investment Securities [Line Items]
Book Value	$ 12,924
Securities available for sale, at fair value	9,075
Unrealized Gain (Loss)	$ (3,849)
Debt Instrument, Credit Rating	B1/CC
Number of Banks (in banks) | Bank	56
Deferrals and Defaults as a % of Current Collateral	15.21%
Excess Subordination as a % of Current Performing Collateral	38.08%
Pooled Trust Preferred Collateralized Debt Obligations [Member] | Mezzanine [Member] | MMCap I [Member]
Impairment Of Investment Securities [Line Items]
Book Value	$ 210
Securities available for sale, at fair value	305
Unrealized Gain (Loss)	$ 95
Debt Instrument, Credit Rating	Ca/C
Number of Banks (in banks) | Bank	8
Deferrals and Defaults as a % of Current Collateral	58.11%
Excess Subordination as a % of Current Performing Collateral	81.96%