Impairment of Investment Securities - Pooled Trust Preferred Collateralized Debt Obligations (Detail) $ in Thousands	3 Months Ended
	Mar. 31, 2017 USD ($) Bank	Dec. 31, 2016 USD ($)
Impairment Of Investment Securities [Line Items]
Securities available for sale, at fair value	$ 832,754	$ 778,612
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax	7,242	7,076
Unrealized Gain (Loss)	16,821	$ 18,546
Pooled Trust Preferred Collateralized Debt Obligations [Member]
Impairment Of Investment Securities [Line Items]
Book Value	40,165
Securities available for sale, at fair value	33,741
Unrealized Gain (Loss)	6,424
Pooled Trust Preferred Collateralized Debt Obligations [Member] | Mezzanine [Member] | Pre TSL IV [Member]
Impairment Of Investment Securities [Line Items]
Book Value	1,827
Securities available for sale, at fair value	1,366
Unrealized Gain (Loss)	$ 461
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	61.36%
Pooled Trust Preferred Collateralized Debt Obligations [Member] | Mezzanine [Member] | Pre TSL VIII [Member]
Impairment Of Investment Securities [Line Items]
Book Value	$ 1,955
Securities available for sale, at fair value	2,142
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax	$ 187
Debt Instrument, Credit Rating	C/C
Number of Banks (in banks) | Bank	27
Deferrals and Defaults as a % of Current Collateral	40.34%
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	$ 2,421
Securities available for sale, at fair value	1,971
Unrealized Gain (Loss)	$ 450
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	10.19%
Pooled Trust Preferred Collateralized Debt Obligations [Member] | Mezzanine [Member] | Pre TSL X [Member]
Impairment Of Investment Securities [Line Items]
Book Value	$ 1,769
Securities available for sale, at fair value	2,024
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax	$ 255
Debt Instrument, Credit Rating	Caa1/C
Number of Banks (in banks) | Bank	42
Deferrals and Defaults as a % of Current Collateral	30.10%
Excess Subordination as a % of Current Performing Collateral	2.11%
Pooled Trust Preferred Collateralized Debt Obligations [Member] | Mezzanine [Member] | Pre TSL XII [Member]
Impairment Of Investment Securities [Line Items]
Book Value	$ 5,940
Securities available for sale, at fair value	4,903
Unrealized Gain (Loss)	$ 1,037
Debt Instrument, Credit Rating	B3/C
Number of Banks (in banks) | Bank	64
Deferrals and Defaults as a % of Current Collateral	24.09%
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	$ 13,010
Securities available for sale, at fair value	11,009
Unrealized Gain (Loss)	$ 2,001
Debt Instrument, Credit Rating	Ba3/CCC
Number of Banks (in banks) | Bank	53
Deferrals and Defaults as a % of Current Collateral	10.01%
Excess Subordination as a % of Current Performing Collateral	55.04%
Pooled Trust Preferred Collateralized Debt Obligations [Member] | Mezzanine [Member] | Pre TSL XIV [Member]
Impairment Of Investment Securities [Line Items]
Book Value	$ 13,030
Securities available for sale, at fair value	10,025
Unrealized Gain (Loss)	$ 3,005
Debt Instrument, Credit Rating	Ba2/CCC
Number of Banks (in banks) | Bank	52
Deferrals and Defaults as a % of Current Collateral	12.87%
Excess Subordination as a % of Current Performing Collateral	38.83%
Pooled Trust Preferred Collateralized Debt Obligations [Member] | Mezzanine [Member] | MMCap I [Member]
Impairment Of Investment Securities [Line Items]
Book Value	$ 213
Securities available for sale, at fair value	301
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax	$ 88
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	85.00%