Fair Value Measurements Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	$ 3,062,143	$ 2,497,537
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgages Held-for-sale, Fair Value Disclosure	83,886	37,828
Estimated Fair Value	3,062,143
Available-for-sale Securities, Fair Value Disclosure		2,497,537
Investments held in Rabbi Trust	24,383	22,213
Derivative assets	339,310	145,595
Assets, Fair Value Disclosure	3,509,722	2,703,173
Liabilities Held-In-Trust, Fair Value Disclosure	24,383	22,213
Derivative Liability	167,785	76,646
Total liabilities	192,168	98,859
State and municipal securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	952,613
Available-for-sale Securities, Fair Value Disclosure		652,927
State and municipal securities | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	952,613
Available-for-sale Securities, Fair Value Disclosure		652,927
Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	367,145
Available-for-sale Securities, Fair Value Disclosure		377,357
Corporate debt securities | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	367,145
Available-for-sale Securities, Fair Value Disclosure		377,357
Collateralized mortgage obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	503,766
Available-for-sale Securities, Fair Value Disclosure		693,718
Collateralized mortgage obligations | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	503,766
Available-for-sale Securities, Fair Value Disclosure		693,718
Residential mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	377,998
Available-for-sale Securities, Fair Value Disclosure		177,312
Residential mortgage-backed securities | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	377,998
Available-for-sale Securities, Fair Value Disclosure		177,312
Commercial mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	762,415
Available-for-sale Securities, Fair Value Disclosure		494,297
Commercial mortgage-backed securities | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	762,415
Available-for-sale Securities, Fair Value Disclosure		494,297
Auction rate securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	98,206
Available-for-sale Securities, Fair Value Disclosure		101,926
Auction rate securities | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	98,206
Available-for-sale Securities, Fair Value Disclosure		101,926
Single-issuer trust preferred securities | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	0	11,200
Level 1 | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgages Held-for-sale, Fair Value Disclosure	0	0
Estimated Fair Value	0
Available-for-sale Securities, Fair Value Disclosure		0
Investments held in Rabbi Trust	24,383	22,213
Derivative assets	323	230
Assets, Fair Value Disclosure	24,706	22,443
Liabilities Held-In-Trust, Fair Value Disclosure	24,383	22,213
Derivative Liability	280	199
Total liabilities	24,663	22,412
Level 1 | State and municipal securities | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	0
Available-for-sale Securities, Fair Value Disclosure		0
Level 1 | Corporate debt securities | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	0
Available-for-sale Securities, Fair Value Disclosure		0
Level 1 | Collateralized mortgage obligations | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	0
Available-for-sale Securities, Fair Value Disclosure		0
Level 1 | Residential mortgage-backed securities | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	0
Available-for-sale Securities, Fair Value Disclosure		0
Level 1 | Commercial mortgage-backed securities | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	0
Available-for-sale Securities, Fair Value Disclosure		0
Level 1 | Auction rate securities | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	0
Available-for-sale Securities, Fair Value Disclosure		0
Level 2 | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgages Held-for-sale, Fair Value Disclosure	83,886	37,828
Estimated Fair Value	2,963,937
Available-for-sale Securities, Fair Value Disclosure		2,393,211
Investments held in Rabbi Trust	0	0
Derivative assets	338,987	145,365
Assets, Fair Value Disclosure	3,386,810	2,576,404
Liabilities Held-In-Trust, Fair Value Disclosure	0	0
Derivative Liability	167,505	76,447
Total liabilities	167,505	76,447
Level 2 | Other Corporate Debt | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	4,400	3,900
Level 2 | Financial Institutions Subordinated Debt | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	362,800	362,300
Level 2 | State and municipal securities | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	952,613
Available-for-sale Securities, Fair Value Disclosure		652,927
Level 2 | Corporate debt securities | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	367,145
Available-for-sale Securities, Fair Value Disclosure		374,957
Level 2 | Collateralized mortgage obligations | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	503,766
Available-for-sale Securities, Fair Value Disclosure		693,718
Level 2 | Residential mortgage-backed securities | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	377,998
Available-for-sale Securities, Fair Value Disclosure		177,312
Level 2 | Commercial mortgage-backed securities | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	762,415
Available-for-sale Securities, Fair Value Disclosure		494,297
Level 2 | Auction rate securities | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	0
Available-for-sale Securities, Fair Value Disclosure		0
Level 2 | Single-issuer trust preferred securities | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	0	8,800
Level 3 | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgages Held-for-sale, Fair Value Disclosure	0	0
Estimated Fair Value	98,206
Available-for-sale Securities, Fair Value Disclosure		104,326
Investments held in Rabbi Trust	0	0
Derivative assets	0	0
Assets, Fair Value Disclosure	98,206	104,326
Liabilities Held-In-Trust, Fair Value Disclosure	0	0
Derivative Liability	0	0
Total liabilities	0	0
Level 3 | State and municipal securities | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	0
Available-for-sale Securities, Fair Value Disclosure		0
Level 3 | Corporate debt securities | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	0
Available-for-sale Securities, Fair Value Disclosure		2,400
Level 3 | Collateralized mortgage obligations | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	0
Available-for-sale Securities, Fair Value Disclosure		0
Level 3 | Residential mortgage-backed securities | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	0
Available-for-sale Securities, Fair Value Disclosure		0
Level 3 | Commercial mortgage-backed securities | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	0
Available-for-sale Securities, Fair Value Disclosure		0
Level 3 | Auction rate securities | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	98,206
Available-for-sale Securities, Fair Value Disclosure		101,926
Level 3 | Single-issuer trust preferred securities | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	$ 0	$ 2,400