Impairment of Investment Securities - Pooled Trust Preferred Collateralized Debt Obligations (Detail) $ in Thousands	6 Months Ended
	Jun. 30, 2017 USD ($) Bank	Dec. 31, 2016 USD ($)
Impairment Of Investment Securities [Line Items]
Securities available for sale, at fair value	$ 786,246	$ 778,612
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax	7,434	7,076
Unrealized Gain (Loss)	15,263	$ 18,546
Pooled Trust Preferred Collateralized Debt Obligations [Member]
Impairment Of Investment Securities [Line Items]
Book Value	40,378
Securities available for sale, at fair value	33,648
Unrealized Gain (Loss)	6,730
Pooled Trust Preferred Collateralized Debt Obligations [Member] | Mezzanine [Member] | Pre TSL IV [Member]
Impairment Of Investment Securities [Line Items]
Book Value	1,823
Securities available for sale, at fair value	1,361
Unrealized Gain (Loss)	$ 462
Debt Instrument, Credit Rating	Ba1/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	60.51%
Pooled Trust Preferred Collateralized Debt Obligations [Member] | Mezzanine [Member] | Pre TSL VIII [Member]
Impairment Of Investment Securities [Line Items]
Book Value	$ 1,983
Securities available for sale, at fair value	2,139
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax	$ 156
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	$ 2,430
Securities available for sale, at fair value	1,965
Unrealized Gain (Loss)	$ 465
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	11.71%
Pooled Trust Preferred Collateralized Debt Obligations [Member] | Mezzanine [Member] | Pre TSL X [Member]
Impairment Of Investment Securities [Line Items]
Book Value	$ 1,801
Securities available for sale, at fair value	2,016
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax	$ 215
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	1.97%
Pooled Trust Preferred Collateralized Debt Obligations [Member] | Mezzanine [Member] | Pre TSL XII [Member]
Impairment Of Investment Securities [Line Items]
Book Value	$ 5,991
Securities available for sale, at fair value	4,913
Unrealized Gain (Loss)	$ 1,078
Debt Instrument, Credit Rating	B3/C
Number of Banks (in banks) | Bank	64
Deferrals and Defaults as a % of Current Collateral	24.13%
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	$ 13,070
Securities available for sale, at fair value	10,965
Unrealized Gain (Loss)	$ 2,105
Debt Instrument, Credit Rating	Ba1/CCC
Number of Banks (in banks) | Bank	52
Deferrals and Defaults as a % of Current Collateral	8.02%
Excess Subordination as a % of Current Performing Collateral	45.06%
Pooled Trust Preferred Collateralized Debt Obligations [Member] | Mezzanine [Member] | Pre TSL XIV [Member]
Impairment Of Investment Securities [Line Items]
Book Value	$ 13,066
Securities available for sale, at fair value	9,983
Unrealized Gain (Loss)	$ 3,083
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	40.25%
Pooled Trust Preferred Collateralized Debt Obligations [Member] | Mezzanine [Member] | MMCap I [Member]
Impairment Of Investment Securities [Line Items]
Book Value	$ 214
Securities available for sale, at fair value	306
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax	$ 92
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	83.52%