Securities - Schedule of Amortized Cost and Fair Value of Available-for-sale and Held-to-maturity Securities (Detail) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015
Schedule of Trading Securities and Other Trading Assets [Line Items]
Available-for-sale, Amortized Cost	$ 1,256,762	$ 1,409,644
Available-for-sale, Gross Unrealized Gains	5,177	8,105
Available-for-sale, Gross Unrealized Losses	(20,763)	(14,680)
Available-for-sale, Estimated Fair Value	1,241,176	1,403,069
Held-to-maturity, Amortized Cost	1,067,967	1,012,930
Held-to-maturity, Gross Unrealized Gains	17,349	28,280
Held-to-maturity, Gross Unrealized Losses	(8,526)	(3,003)
Held-to-maturity securities, Fair value	1,076,790	1,038,207
Total, Amortized Cost	2,324,729	2,422,574
Total, Gross Unrealized Gains	22,526	36,385
Total, Gross Unrealized Losses	(29,289)	(17,683)
Total, Estimated Fair Value	2,317,966	2,441,276
U.S. Government Sponsored Entities and Agencies [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Available-for-sale, Amortized Cost	54,803	82,725
Available-for-sale, Gross Unrealized Gains	3	1,183
Available-for-sale, Gross Unrealized Losses	(763)	(403)
Available-for-sale, Estimated Fair Value	54,043	83,505
Held-to-maturity, Amortized Cost	13,394
Held-to-maturity, Gross Unrealized Losses	(414)
Held-to-maturity securities, Fair value	12,980
Residential Mortgage-Backed Securities and Collateralized Mortgage Obligations of Government Agencies [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Available-for-sale, Amortized Cost	1,052,397	1,188,256
Available-for-sale, Gross Unrealized Gains	911	1,720
Available-for-sale, Gross Unrealized Losses	(18,209)	(13,896)
Available-for-sale, Estimated Fair Value	1,035,099	1,176,080
Held-to-maturity, Amortized Cost	215,141	216,419
Held-to-maturity, Gross Unrealized Gains	1,279	1,922
Held-to-maturity, Gross Unrealized Losses	(2,563)	(2,014)
Held-to-maturity securities, Fair value	213,857	216,327
Obligations of State and Political Subdivisions [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Available-for-sale, Amortized Cost	110,208	76,106
Available-for-sale, Gross Unrealized Gains	3,114	4,205
Available-for-sale, Gross Unrealized Losses	(1,659)	(46)
Available-for-sale, Estimated Fair Value	111,663	80,265
Held-to-maturity, Amortized Cost	805,019	762,039
Held-to-maturity, Gross Unrealized Gains	15,652	26,121
Held-to-maturity, Gross Unrealized Losses	(5,529)	(726)
Held-to-maturity securities, Fair value	815,142	787,434
Corporate Debt Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Available-for-sale, Amortized Cost	35,292	58,745
Available-for-sale, Gross Unrealized Gains	117	181
Available-for-sale, Gross Unrealized Losses	(108)	(333)
Available-for-sale, Estimated Fair Value	35,301	58,593
Held-to-maturity, Amortized Cost	34,413	34,472
Held-to-maturity, Gross Unrealized Gains	418	237
Held-to-maturity, Gross Unrealized Losses	(20)	(263)
Held-to-maturity securities, Fair value	34,811	34,446
Debt Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Available-for-sale, Amortized Cost	1,252,700	1,405,832
Available-for-sale, Gross Unrealized Gains	4,145	7,289
Available-for-sale, Gross Unrealized Losses	(20,739)	(14,678)
Available-for-sale, Estimated Fair Value	1,236,106	1,398,443
Equity Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Available-for-sale, Amortized Cost	4,062	3,812
Available-for-sale, Gross Unrealized Gains	1,032	816
Available-for-sale, Gross Unrealized Losses	(24)	(2)
Available-for-sale, Estimated Fair Value	$ 5,070	$ 4,626

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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-Publisher FASB
-Name Accounting Standards Codification
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Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

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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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Amount of accumulated unrealized gain on investments in debt securities classified as held-to-maturity.

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Amount of accumulated unrealized loss on investments in debt securities classified as held-to-maturity.

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Fair value of investments in debt securities classified as held-to-maturity.

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Fair value portion of investment securities, including, but not limited to, marketable securities, derivative financial instruments, and investments accounted for under the equity method.

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The increase (decrease), resulting in a gain, in the difference between the fair value and the carrying value, or in the comparative fair values, of securities held at each balance sheet date, that was included in earnings for the period.

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Securities amortized cost.

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