Contractual Maturity Information for Securities Held to Maturity (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Investments, Debt and Equity Securities [Abstract]
Due in 1 year or less, Amortized Cost	$ 6,077	$ 17,265
Due after 1 year through 5 years, Amortized Cost	82,650	77,237
Due after 5 years through 10 years, Amortized Cost	341,741	370,631
Due after 10 years, Amortized Cost	685,464	201,973
Total securities held to maturity, Amortized Cost	1,115,932	667,106
Due in 1 year or less, Gross Unrealized Gains	5
Due after 1 year through 5 years, Gross Unrealized Gains	2,376
Due after 5 years through 10 years, Gross Unrealized Gains	8,854
Due after 10 years, Gross Unrealized Gains	15,717
Total securities held to maturity, Gross Unrealized Gains	26,952
Due in 1 year or less, Gross Unrealized Losses	(947)
Due after 1 year through 5 years, Gross Unrealized Losses	(1,474)
Due after 5 years through 10 years, Gross Unrealized Losses	(3,021)
Due after 10 years, Gross Unrealized Losses	(31,415)
Total securities held to maturity, Gross Unrealized Losses	(36,857)
Due in 1 year or less, Fair Value	5,135	17,893
Due after 1 year through 5 years, Fair Value	83,552	80,047
Due after 5 years through 10 years, Fair Value	347,574	384,117
Due after 10 years, Fair Value	669,766	209,322
Total securities held to maturity, Fair Value	$ 1,106,027	691,379
Due in 1 year or less, Net Unrealized Gains		628
Due after 1 year through 5 years, Net Unrealized Gains		2,810
Due after 5 years through 10 years, Net Unrealized Gains		13,486
Due after 10 years, Net Unrealized Gains		7,349
Total securities held to maturity, Net Unrealized Gains		$ 24,273

Held To Maturity Securities Debt Maturities After Five Through Ten Years Accumulated Unrealized Gains

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Amount after other than temporary impairment (OTTI) accretion, of investments in debt securities classified as held-to-maturity.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
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Amount of accumulated unrealized gain on investments in debt securities classified as held-to-maturity.

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Fair value of held-to-maturity debt securities maturing in the sixth fiscal year through the tenth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Carrying amount of debt securities accounted for as held-to-maturity, net of adjustments including, but not limited to, accretion, amortization, collection of cash, previous other-than-temporary impairments (OTTI) recognized, and fair value hedge accounting adjustments, maturing in the fifth through tenth fiscal year following the latest fiscal year.

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Fair value of held-to-maturity debt securities maturing in the second fiscal year through the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Carrying amount of debt securities accounted for as held-to-maturity, net of adjustments including, but not limited to, accretion, amortization, collection of cash, previous other-than-temporary impairments (OTTI) recognized, and fair value hedge accounting adjustments, maturing in the next fiscal year through the fifth fiscal year following the latest fiscal year.

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Fair value of held-to-maturity debt securities maturing after the tenth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Fair value of held-to-maturity debt securities maturing in the next fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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