Impairment of Investment Securities - Pooled Trust Preferred Collateralized Debt Obligations (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2016 USD ($) Bank	Dec. 31, 2015 USD ($)
Impairment Of Investment Securities [Line Items]
Amortized Cost	$ 790,082	$ 891,111
Estimated Fair Value of Available for Sale	778,612	$ 886,560
Mezzanine [Member]
Impairment Of Investment Securities [Line Items]
Amortized Cost	39,989
Estimated Fair Value of Available for Sale	33,292
Unrealized Gain (Loss)	(6,697)
Mezzanine [Member] | Pre TSL IV [Member]
Impairment Of Investment Securities [Line Items]
Amortized Cost	1,830
Estimated Fair Value of Available for Sale	1,360
Unrealized Gain (Loss)	$ (470)
Debt Instrument, Credit Rating	B1/BB
Number of Banks | Bank	6
Deferrals and Defaults as a % of Current Collateral	18.05%
Excess Subordination as a % of Current Performing Collateral	59.78%
Mezzanine [Member] | Pre TSL VII [Member]
Impairment Of Investment Securities [Line Items]
Amortized Cost	$ 3,100
Mezzanine [Member] | Pre TSL VIII [Member]
Impairment Of Investment Securities [Line Items]
Amortized Cost	1,963
Estimated Fair Value of Available for Sale	2,053
Unrealized Gain (Loss)	$ 90
Debt Instrument, Credit Rating	C/C
Number of Banks | Bank	28
Deferrals and Defaults as a % of Current Collateral	44.37%
Excess Subordination as a % of Current Performing Collateral	0.00%
Mezzanine [Member] | Pre TSL IX [Member]
Impairment Of Investment Securities [Line Items]
Amortized Cost	$ 2,412
Estimated Fair Value of Available for Sale	1,952
Unrealized Gain (Loss)	$ (460)
Debt Instrument, Credit Rating	B1/C
Number of Banks | Bank	37
Deferrals and Defaults as a % of Current Collateral	27.83%
Excess Subordination as a % of Current Performing Collateral	12.79%
Mezzanine [Member] | Pre TSL X [Member]
Impairment Of Investment Securities [Line Items]
Amortized Cost	$ 1,738
Estimated Fair Value of Available for Sale	1,986
Unrealized Gain (Loss)	$ 248
Debt Instrument, Credit Rating	Caa1/C
Number of Banks | Bank	42
Deferrals and Defaults as a % of Current Collateral	31.58%
Excess Subordination as a % of Current Performing Collateral	2.17%
Mezzanine [Member] | Pre TSL XII [Member]
Impairment Of Investment Securities [Line Items]
Amortized Cost	$ 5,890
Estimated Fair Value of Available for Sale	4,817
Unrealized Gain (Loss)	$ (1,073)
Debt Instrument, Credit Rating	B3/C
Number of Banks | Bank	64
Deferrals and Defaults as a % of Current Collateral	24.54%
Excess Subordination as a % of Current Performing Collateral	0.00%
Mezzanine [Member] | Pre TSL XIII [Member]
Impairment Of Investment Securities [Line Items]
Amortized Cost	$ 12,949
Estimated Fair Value of Available for Sale	10,900
Unrealized Gain (Loss)	$ (2,049)
Debt Instrument, Credit Rating	Ba3/C
Number of Banks | Bank	54
Deferrals and Defaults as a % of Current Collateral	11.21%
Excess Subordination as a % of Current Performing Collateral	55.77%
Mezzanine [Member] | Pre TSL XIV [Member]
Impairment Of Investment Securities [Line Items]
Amortized Cost	$ 12,995
Estimated Fair Value of Available for Sale	9,923
Unrealized Gain (Loss)	$ (3,072)
Debt Instrument, Credit Rating	B1/CC
Number of Banks | Bank	52
Deferrals and Defaults as a % of Current Collateral	12.78%
Excess Subordination as a % of Current Performing Collateral	31.90%
Mezzanine [Member] | MMCap I [Member]
Impairment Of Investment Securities [Line Items]
Amortized Cost	$ 212
Estimated Fair Value of Available for Sale	301
Unrealized Gain (Loss)	$ 89
Debt Instrument, Credit Rating	Ca/C
Number of Banks | Bank	8
Deferrals and Defaults as a % of Current Collateral	58.11%
Excess Subordination as a % of Current Performing Collateral	80.31%