Securities - Summaries of Fair Values and Unrealized Losses of Impaired Securities, Segregated by Length of Impairment (Detail) $ in Thousands	Jun. 30, 2016 USD ($) Security	Dec. 31, 2015 USD ($) Security
Schedule Of Securities [Line Items]
Number of available for sale securities, Less than 1 year \| Security	11	36
Number of available for sale securities, Greater than 1 year \| Security	14	23
Number of available for sale securities \| Security	25	59
Securities Available For Sale, Less than 12 Months, Fair Value	$ 24,698	$ 589,609
Securities Available For Sale, Less than 12 Months, Unrealized Losses	(120)	(5,027)
Securities Available For Sale, 12 Months or More, Fair Value	126,709	254,062
Securities Available For Sale, 12 Months or More, Unrealized Losses	(2,258)	(8,326)
Securities Available For Sale, Fair Value, Total	151,407	843,671
Securities Available For Sale, Unrealized Losses, Total	$ (2,378)	$ (13,353)
Number of held to maturity securities \| Security	15	59
Securities Held To Maturity, Less than 12 Months, Fair Value	$ 9,715	$ 466,354
Securities Held To Maturity, Less than 12 Months, Unrealized Losses	(85)	(3,126)
Securities Held To Maturity, Greater than 12 Months, Fair Value	128,715	176,411
Securities Held To Maturity, Greater than 12 Months, Unrealized Losses	(1,305)	(6,462)
Securities Held To Maturity, Fair Value, Total	138,430	642,765
Securities Held To Maturity, Unrealized Losses, Total	$ (1,390)	$ (9,588)
Less than 12 Months [Member]
Schedule Of Securities [Line Items]
Number of held to maturity securities \| Security	3	43
Greater than 12 Months [Member]
Schedule Of Securities [Line Items]
Number of held to maturity securities \| Security	12	16
U.S. Government-Sponsored Entities [Member]
Schedule Of Securities [Line Items]
Number of available for sale securities, Less than 1 year \| Security		6
Number of available for sale securities, Greater than 1 year \| Security		2
Number of available for sale securities \| Security		8
Securities Available For Sale, Less than 12 Months, Fair Value		$ 99,131
Securities Available For Sale, Less than 12 Months, Unrealized Losses		(814)
Securities Available For Sale, 12 Months or More, Fair Value		34,487
Securities Available For Sale, 12 Months or More, Unrealized Losses		(511)
Securities Available For Sale, Fair Value, Total		133,618
Securities Available For Sale, Unrealized Losses, Total		$ (1,325)
Number of held to maturity securities \| Security		4
Securities Held To Maturity, Less than 12 Months, Fair Value		$ 39,843
Securities Held To Maturity, Less than 12 Months, Unrealized Losses		(173)
Securities Held To Maturity, Greater than 12 Months, Fair Value		14,778
Securities Held To Maturity, Greater than 12 Months, Unrealized Losses		(222)
Securities Held To Maturity, Fair Value, Total		54,621
Securities Held To Maturity, Unrealized Losses, Total		$ (395)
U.S. Government-Sponsored Entities [Member] \| Less than 12 Months [Member]
Schedule Of Securities [Line Items]
Number of held to maturity securities \| Security		3
U.S. Government-Sponsored Entities [Member] \| Greater than 12 Months [Member]
Schedule Of Securities [Line Items]
Number of held to maturity securities \| Security		1
Agency Mortgage-Backed Securities [Member]
Schedule Of Securities [Line Items]
Number of available for sale securities, Less than 1 year \| Security		19
Number of available for sale securities \| Security		19
Securities Available For Sale, Less than 12 Months, Fair Value		$ 359,250
Securities Available For Sale, Less than 12 Months, Unrealized Losses		(2,832)
Securities Available For Sale, Fair Value, Total		359,250
Securities Available For Sale, Unrealized Losses, Total		$ (2,832)
Number of held to maturity securities \| Security		18
Securities Held To Maturity, Less than 12 Months, Fair Value		$ 212,024
Securities Held To Maturity, Less than 12 Months, Unrealized Losses		(1,159)
Securities Held To Maturity, Greater than 12 Months, Fair Value		917
Securities Held To Maturity, Greater than 12 Months, Unrealized Losses		(17)
Securities Held To Maturity, Fair Value, Total		212,941
Securities Held To Maturity, Unrealized Losses, Total		$ (1,176)
Agency Mortgage-Backed Securities [Member] \| Less than 12 Months [Member]
Schedule Of Securities [Line Items]
Number of held to maturity securities \| Security		17
Agency Mortgage-Backed Securities [Member] \| Greater than 12 Months [Member]
Schedule Of Securities [Line Items]
Number of held to maturity securities \| Security		1
Agency Collateralized Mortgage Obligations [Member]
Schedule Of Securities [Line Items]
Number of available for sale securities, Less than 1 year \| Security	1	9
Number of available for sale securities, Greater than 1 year \| Security	11	18
Number of available for sale securities \| Security	12	27
Securities Available For Sale, Less than 12 Months, Fair Value	$ 12,209	$ 126,309
Securities Available For Sale, Less than 12 Months, Unrealized Losses	(37)	(1,366)
Securities Available For Sale, 12 Months or More, Fair Value	122,569	215,330
Securities Available For Sale, 12 Months or More, Unrealized Losses	(1,498)	(7,164)
Securities Available For Sale, Fair Value, Total	134,778	341,639
Securities Available For Sale, Unrealized Losses, Total	$ (1,535)	$ (8,530)
Number of held to maturity securities \| Security	12	25
Securities Held To Maturity, Less than 12 Months, Fair Value		$ 150,593
Securities Held To Maturity, Less than 12 Months, Unrealized Losses		(1,434)
Securities Held To Maturity, Greater than 12 Months, Fair Value	$ 128,715	160,716
Securities Held To Maturity, Greater than 12 Months, Unrealized Losses	(1,305)	(6,223)
Securities Held To Maturity, Fair Value, Total	128,715	311,309
Securities Held To Maturity, Unrealized Losses, Total	$ (1,305)	$ (7,657)
Agency Collateralized Mortgage Obligations [Member] \| Less than 12 Months [Member]
Schedule Of Securities [Line Items]
Number of held to maturity securities \| Security		11
Agency Collateralized Mortgage Obligations [Member] \| Greater than 12 Months [Member]
Schedule Of Securities [Line Items]
Number of held to maturity securities \| Security	12	14
Non-Agency Collateralized Mortgage Obligations [Member]
Schedule Of Securities [Line Items]
Number of available for sale securities, Less than 1 year \| Security	1
Number of available for sale securities \| Security	1
Securities Available For Sale, Less than 12 Months, Fair Value	$ 974
Securities Available For Sale, Less than 12 Months, Unrealized Losses	(56)
Securities Available For Sale, Fair Value, Total	974
Securities Available For Sale, Unrealized Losses, Total	$ (56)
Number of held to maturity securities \| Security	2
Securities Held To Maturity, Less than 12 Months, Fair Value	$ 1,174
Securities Held To Maturity, Less than 12 Months, Unrealized Losses	(4)
Securities Held To Maturity, Fair Value, Total	1,174
Securities Held To Maturity, Unrealized Losses, Total	$ (4)
Non-Agency Collateralized Mortgage Obligations [Member] \| Less than 12 Months [Member]
Schedule Of Securities [Line Items]
Number of held to maturity securities \| Security	2
Commercial Mortgage-Backed Securities [Member]
Schedule Of Securities [Line Items]
Number of available for sale securities, Less than 1 year \| Security		1
Number of available for sale securities \| Security		1
Securities Available For Sale, Less than 12 Months, Fair Value		$ 4,287
Securities Available For Sale, Less than 12 Months, Unrealized Losses		(12)
Securities Available For Sale, Fair Value, Total		4,287
Securities Available For Sale, Unrealized Losses, Total		$ (12)
Number of held to maturity securities \| Security	1	3
Securities Held To Maturity, Less than 12 Months, Fair Value	$ 8,541	$ 46,278
Securities Held To Maturity, Less than 12 Months, Unrealized Losses	(81)	(259)
Securities Held To Maturity, Fair Value, Total	8,541	46,278
Securities Held To Maturity, Unrealized Losses, Total	$ (81)	$ (259)
Commercial Mortgage-Backed Securities [Member] \| Less than 12 Months [Member]
Schedule Of Securities [Line Items]
Number of held to maturity securities \| Security	1	3
States of the U.S. and Political Subdivisions [Member]
Schedule Of Securities [Line Items]
Number of available for sale securities, Less than 1 year \| Security	9
Number of available for sale securities \| Security	9
Securities Available For Sale, Less than 12 Months, Fair Value	$ 11,515
Securities Available For Sale, Less than 12 Months, Unrealized Losses	(27)
Securities Available For Sale, Fair Value, Total	11,515
Securities Available For Sale, Unrealized Losses, Total	$ (27)
Number of held to maturity securities \| Security		9
Securities Held To Maturity, Less than 12 Months, Fair Value		$ 17,616
Securities Held To Maturity, Less than 12 Months, Unrealized Losses		(101)
Securities Held To Maturity, Fair Value, Total		17,616
Securities Held To Maturity, Unrealized Losses, Total		$ (101)
States of the U.S. and Political Subdivisions [Member] \| Less than 12 Months [Member]
Schedule Of Securities [Line Items]
Number of held to maturity securities \| Security		9
Other Securities [Member]
Schedule Of Securities [Line Items]
Number of available for sale securities, Greater than 1 year \| Security	3	3
Number of available for sale securities \| Security	3	3
Securities Available For Sale, 12 Months or More, Fair Value	$ 4,140	$ 4,245
Securities Available For Sale, 12 Months or More, Unrealized Losses	(760)	(651)
Securities Available For Sale, Fair Value, Total	4,140	4,245
Securities Available For Sale, Unrealized Losses, Total	$ (760)	$ (651)
Equity Securities [Member]
Schedule Of Securities [Line Items]
Number of available for sale securities, Less than 1 year \| Security		1
Number of available for sale securities \| Security		1
Securities Available For Sale, Less than 12 Months, Fair Value		$ 632
Securities Available For Sale, Less than 12 Months, Unrealized Losses		(3)
Securities Available For Sale, Fair Value, Total		632
Securities Available For Sale, Unrealized Losses, Total		$ (3)

Schedule Of Securities [Line Items]

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Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale that have been in a continuous loss position for twelve months or longer.

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-Publisher FASB
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Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale in a continuous loss position.

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This item represents the aggregate fair value of investments in debt and equity securities in an unrealized loss position which are categorized neither as held-to-maturity nor trading securities.

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Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale that have been in a continuous loss position for less than twelve months.

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Number of investment positions in available-for-sale investments in a continuous unrealized loss position for less than one year or normal operating cycle, if longer, for which an other-than-temporary impairment (OTTI) has not been recognized in the income statement.

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Amount of accumulated unrealized loss on investments in debt securities classified as held-to-maturity that have been in a continuous loss position for twelve months or longer.

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Disclosure regarding factors used to determine that the impairment of securities categorized as held-to-maturity where cost exceeds fair value is not an other than temporary impairment (OTTI). This item contains disclosure of the number of investment positions in the held-to-maturity investments determined to be temporarily impaired.

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