Estimated Fair Value Of Financial Instruments (Fair Value Measurements On A Recurring Basis) (Detail) - USD ($) $ in Thousands		Sep. 30, 2016		Dec. 31, 2015
Estimated Fair Value Of Financial Instruments [Line Items]
Securities Available-for-Sale, Fair Value		$ 1,961,099		$ 1,765,366
Mortgage loans held-for-sale		28,492		35,704
Loans Receivable, Fair Value Disclosure		1,050	[1]	0
Interest rate contract derivatives assets designated as hedging instruments		4,624		5,366
Other derivative assets, not designated as hedging instruments		66,633		47,487
Netting adjustments	[2],[3],[4]	(9,163)		(12,238)
Derivative assets	[2]	62,094		40,615
Total assets		2,052,735		1,841,685
Interest rate contract derivatives liabilities designated as hedging instruments		0		799
Netting adjustments	[2],[3],[4]	(49,021)		(30,056)
Derivative liabilities	[2]	19,236		18,229
Fair Value, Inputs, Level 1 [Member]
Estimated Fair Value Of Financial Instruments [Line Items]
Securities Available-for-Sale, Fair Value		477,601		321,651
Mortgage loans held-for-sale		0		0
Loans Receivable, Fair Value Disclosure		0		0
Derivative assets		0		0
Total assets		477,601		321,651
Derivative liabilities		0		0
Fair Value, Inputs, Level 2 [Member]
Estimated Fair Value Of Financial Instruments [Line Items]
Securities Available-for-Sale, Fair Value		1,483,498		1,443,085
Mortgage loans held-for-sale		28,492		35,704
Loans Receivable, Fair Value Disclosure		1,050	[1]	0
Interest rate contract derivatives assets designated as hedging instruments		4,624		5,366
Netting adjustments		(9,163)		(12,167)
Derivative assets		60,990		39,795
Total assets		1,574,030		1,518,584
Interest rate contract derivatives liabilities designated as hedging instruments		0		799
Netting adjustments		(49,021)		(29,974)
Derivative liabilities		19,035		18,046
Fair Value, Inputs, Level 3 [Member]
Estimated Fair Value Of Financial Instruments [Line Items]
Securities Available-for-Sale, Fair Value		0		630
Mortgage loans held-for-sale		0		0
Loans Receivable, Fair Value Disclosure		14,370,031		12,929,340
Netting adjustments		0		(71)
Derivative assets		1,104		820
Total assets		1,104		1,450
Netting adjustments		0		(82)
Derivative liabilities		201		183
U.S. Treasury [Member]
Estimated Fair Value Of Financial Instruments [Line Items]
Securities Available-for-Sale, Fair Value		477,601		321,651
U.S. Treasury [Member] | Fair Value, Inputs, Level 1 [Member]
Estimated Fair Value Of Financial Instruments [Line Items]
Securities Available-for-Sale, Fair Value		477,601		321,651
U.S. Agencies [Member]
Estimated Fair Value Of Financial Instruments [Line Items]
Securities Available-for-Sale, Fair Value		46,556		46,098
U.S. Agencies [Member] | Fair Value, Inputs, Level 2 [Member]
Estimated Fair Value Of Financial Instruments [Line Items]
Securities Available-for-Sale, Fair Value		46,556		46,098
Collateralized mortgage obligations [Member]
Estimated Fair Value Of Financial Instruments [Line Items]
Securities Available-for-Sale, Fair Value		82,265		99,972
Collateralized mortgage obligations [Member] | Fair Value, Inputs, Level 2 [Member]
Estimated Fair Value Of Financial Instruments [Line Items]
Securities Available-for-Sale, Fair Value		82,265		99,972
Residential mortgage-backed securities [Member]
Estimated Fair Value Of Financial Instruments [Line Items]
Securities Available-for-Sale, Fair Value		878,963		829,855
Residential mortgage-backed securities [Member] | Fair Value, Inputs, Level 2 [Member]
Estimated Fair Value Of Financial Instruments [Line Items]
Securities Available-for-Sale, Fair Value		878,963		829,855
State and municipal securities [Member]
Estimated Fair Value Of Financial Instruments [Line Items]
Securities Available-for-Sale, Fair Value		475,714		467,790
State and municipal securities [Member] | Fair Value, Inputs, Level 2 [Member]
Estimated Fair Value Of Financial Instruments [Line Items]
Securities Available-for-Sale, Fair Value		475,714		467,160
State and municipal securities [Member] | Fair Value, Inputs, Level 3 [Member]
Estimated Fair Value Of Financial Instruments [Line Items]
Securities Available-for-Sale, Fair Value		0		630
Client-Related Derivatives [Member]
Estimated Fair Value Of Financial Instruments [Line Items]
Other derivative assets, not designated as hedging instruments		65,233		46,748
Other derivatives liabilities, not designated as hedging instruments		67,842		47,302
Client-Related Derivatives [Member] | Fair Value, Inputs, Level 2 [Member]
Estimated Fair Value Of Financial Instruments [Line Items]
Other derivative assets, not designated as hedging instruments		64,514		46,342
Other derivatives liabilities, not designated as hedging instruments		67,814		47,204
Client-Related Derivatives [Member] | Fair Value, Inputs, Level 3 [Member]
Estimated Fair Value Of Financial Instruments [Line Items]
Other derivative assets, not designated as hedging instruments		719		406
Other derivatives liabilities, not designated as hedging instruments		28		98
Other End-User Derivatives [Member]
Estimated Fair Value Of Financial Instruments [Line Items]
Other derivative assets, not designated as hedging instruments		1,400		739
Other derivatives liabilities, not designated as hedging instruments		415		184
Other End-User Derivatives [Member] | Fair Value, Inputs, Level 2 [Member]
Estimated Fair Value Of Financial Instruments [Line Items]
Other derivative assets, not designated as hedging instruments		1,015		254
Other derivatives liabilities, not designated as hedging instruments		242		17
Other End-User Derivatives [Member] | Fair Value, Inputs, Level 3 [Member]
Estimated Fair Value Of Financial Instruments [Line Items]
Other derivative assets, not designated as hedging instruments		385		485
Other derivatives liabilities, not designated as hedging instruments		$ 173		$ 167

[1] Represents loans accounted for under the fair value option.

[2] All derivative contracts are over-the-counter contracts.

[3] Represents financial instrument and related cash collateral entered into with the same counterparty and subject to a master netting agreement.

[4] Represents netting of derivative asset and liability balances, and related cash collateral, with the same counterparty subject to master netting agreements. Refer to Note 15 for additional information regarding master netting agreements.