Impairment of Investment Securities - Pooled Trust Preferred Collateralized Debt Obligations (Detail) $ in Thousands	9 Months Ended
	Sep. 30, 2016 USD ($) Bank	Dec. 31, 2015 USD ($)
Impairment Of Investment Securities [Line Items]
Securities available for sale, at fair value	$ 813,659	$ 886,560
Unrealized Gain (Loss)	8,644	$ 16,477
Pooled Trust Preferred Collateralized Debt Obligations [Member]
Impairment Of Investment Securities [Line Items]
Book Value	43,020
Securities available for sale, at fair value	35,609
Unrealized Gain (Loss)	(7,411)
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	1,331
Unrealized Gain (Loss)	$ (499)
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	60.61%
Pooled Trust Preferred Collateralized Debt Obligations [Member] | Mezzanine [Member] | Pre TSL VII [Member]
Impairment Of Investment Securities [Line Items]
Book Value	$ 3,119
Securities available for sale, at fair value	3,513
Unrealized Gain (Loss)	$ 394
Debt Instrument, Credit Rating	Ca/-
Number of Banks (in banks) | Bank	14
Deferrals and Defaults as a % of Current Collateral	47.77%
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	$ 2,063
Securities available for sale, at fair value	2,025
Unrealized Gain (Loss)	$ (38)
Debt Instrument, Credit Rating	C/C
Number of Banks (in banks) | Bank	28
Deferrals and Defaults as a % of Current Collateral	44.37%
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	$ 2,403
Securities available for sale, at fair value	1,893
Unrealized Gain (Loss)	$ (510)
Debt Instrument, Credit Rating	B1/C
Number of Banks (in banks) | Bank	37
Deferrals and Defaults as a % of Current Collateral	27.83%
Excess Subordination as a % of Current Performing Collateral	12.79%
Pooled Trust Preferred Collateralized Debt Obligations [Member] | Mezzanine [Member] | Pre TSL X [Member]
Impairment Of Investment Securities [Line Items]
Book Value	$ 1,707
Securities available for sale, at fair value	1,887
Unrealized Gain (Loss)	$ 180
Debt Instrument, Credit Rating	Caa1/C
Number of Banks (in banks) | Bank	42
Deferrals and Defaults as a % of Current Collateral	31.58%
Excess Subordination as a % of Current Performing Collateral	2.17%
Pooled Trust Preferred Collateralized Debt Obligations [Member] | Mezzanine [Member] | Pre TSL XII [Member]
Impairment Of Investment Securities [Line Items]
Book Value	$ 5,839
Securities available for sale, at fair value	4,584
Unrealized Gain (Loss)	$ (1,255)
Debt Instrument, Credit Rating	B3/C
Number of Banks (in banks) | Bank	64
Deferrals and Defaults as a % of Current Collateral	24.50%
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	$ 12,888
Securities available for sale, at fair value	10,504
Unrealized Gain (Loss)	$ (2,384)
Debt Instrument, Credit Rating	Ba3/C
Number of Banks (in banks) | Bank	54
Deferrals and Defaults as a % of Current Collateral	11.75%
Excess Subordination as a % of Current Performing Collateral	48.41%
Pooled Trust Preferred Collateralized Debt Obligations [Member] | Mezzanine [Member] | Pre TSL XIV [Member]
Impairment Of Investment Securities [Line Items]
Book Value	$ 12,960
Securities available for sale, at fair value	9,559
Unrealized Gain (Loss)	$ (3,401)
Debt Instrument, Credit Rating	B1/CC
Number of Banks (in banks) | Bank	54
Deferrals and Defaults as a % of Current Collateral	13.45%
Excess Subordination as a % of Current Performing Collateral	37.92%
Pooled Trust Preferred Collateralized Debt Obligations [Member] | Mezzanine [Member] | MMCap I [Member]
Impairment Of Investment Securities [Line Items]
Book Value	$ 211
Securities available for sale, at fair value	313
Unrealized Gain (Loss)	$ 102
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	81.65%