Fair Value Measurements Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	$ 2,315,541	$ 2,080,294
Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	2,315,541
Mortgages Held-for-sale, Fair Value Disclosure	33,945	27,099
Available-for-sale Securities, Fair Value Disclosure		2,080,294
Investments held in Rabbi Trust	20,853	18,415
Derivative assets	195,798	62,944
Assets, Fair Value Disclosure	2,566,137	2,188,752
Liabilities Held-In-Trust, Fair Value Disclosure	20,853	18,415
Derivative Liability	105,496	48,566
Total liabilities	126,349	66,981
U.S. Government-Sponsored Agency Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure		31,632
U.S. Government-Sponsored Agency Securities [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure		31,632
US States and Political Subdivisions Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	547,344
Available-for-sale Securities, Fair Value Disclosure		279,095
US States and Political Subdivisions Debt Securities [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	547,344
Available-for-sale Securities, Fair Value Disclosure		279,095
Corporate Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	358,406
Available-for-sale Securities, Fair Value Disclosure		109,533
Corporate Debt Securities [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	358,406
Available-for-sale Securities, Fair Value Disclosure		109,533
Collateralized Mortgage Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	700,599
Available-for-sale Securities, Fair Value Disclosure		832,080
Collateralized Mortgage Obligations [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	700,599
Available-for-sale Securities, Fair Value Disclosure		832,080
Mortgage-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	183,785
Available-for-sale Securities, Fair Value Disclosure		463,344
Mortgage-Backed Securities [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	183,785
Available-for-sale Securities, Fair Value Disclosure		463,344
Commercial Mortgage Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	422,109
Available-for-sale Securities, Fair Value Disclosure		261,616
Commercial Mortgage Backed Securities [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	422,109
Available-for-sale Securities, Fair Value Disclosure		261,616
Auction Rate Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	103,298
Available-for-sale Securities, Fair Value Disclosure		102,994
Auction Rate Securities [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	103,298
Available-for-sale Securities, Fair Value Disclosure		102,994
Single-issuer Trust Preferred Securities [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	18,500	18,600
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	0
Mortgages Held-for-sale, Fair Value Disclosure	0	0
Available-for-sale Securities, Fair Value Disclosure		0
Investments held in Rabbi Trust	20,853	18,415
Derivative assets	535	392
Assets, Fair Value Disclosure	21,388	18,807
Liabilities Held-In-Trust, Fair Value Disclosure	20,853	18,415
Derivative Liability	480	381
Total liabilities	21,333	18,796
Fair Value, Inputs, Level 1 [Member] | U.S. Government-Sponsored Agency Securities [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure		0
Fair Value, Inputs, Level 1 [Member] | US States and Political Subdivisions Debt Securities [Member] | Fair Value, Measurements, Recurring [Member]
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
Fair Value, Inputs, Level 1 [Member] | Corporate Debt Securities [Member] | Fair Value, Measurements, Recurring [Member]
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
Fair Value, Inputs, Level 1 [Member] | Collateralized Mortgage Obligations [Member] | Fair Value, Measurements, Recurring [Member]
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
Fair Value, Inputs, Level 1 [Member] | Mortgage-Backed Securities [Member] | Fair Value, Measurements, Recurring [Member]
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
Fair Value, Inputs, Level 1 [Member] | Commercial Mortgage Backed Securities [Member] | Fair Value, Measurements, Recurring [Member]
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
Fair Value, Inputs, Level 1 [Member] | Auction Rate Securities [Member] | Fair Value, Measurements, Recurring [Member]
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
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	2,209,873
Mortgages Held-for-sale, Fair Value Disclosure	33,945	27,099
Available-for-sale Securities, Fair Value Disclosure		1,974,025
Investments held in Rabbi Trust	0	0
Derivative assets	195,263	62,552
Assets, Fair Value Disclosure	2,439,081	2,063,676
Liabilities Held-In-Trust, Fair Value Disclosure	0	0
Derivative Liability	105,016	48,185
Total liabilities	105,016	48,185
Fair Value, Inputs, Level 2 [Member] | Other Corporate Debt [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	3,900	3,900
Fair Value, Inputs, Level 2 [Member] | Financial Institutions Subordinated Debt [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	336,000	86,100
Fair Value, Inputs, Level 2 [Member] | U.S. Government-Sponsored Agency Securities [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure		31,632
Fair Value, Inputs, Level 2 [Member] | US States and Political Subdivisions Debt Securities [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	547,344
Available-for-sale Securities, Fair Value Disclosure		279,095
Fair Value, Inputs, Level 2 [Member] | Corporate Debt Securities [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	356,036
Available-for-sale Securities, Fair Value Disclosure		106,258
Fair Value, Inputs, Level 2 [Member] | Collateralized Mortgage Obligations [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	700,599
Available-for-sale Securities, Fair Value Disclosure		832,080
Fair Value, Inputs, Level 2 [Member] | Mortgage-Backed Securities [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	183,785
Available-for-sale Securities, Fair Value Disclosure		463,344
Fair Value, Inputs, Level 2 [Member] | Commercial Mortgage Backed Securities [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	422,109
Available-for-sale Securities, Fair Value Disclosure		261,616
Fair Value, Inputs, Level 2 [Member] | Auction Rate Securities [Member] | Fair Value, Measurements, Recurring [Member]
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
Fair Value, Inputs, Level 2 [Member] | Single-issuer Trust Preferred Securities [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	16,100	16,300
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	105,668
Mortgages Held-for-sale, Fair Value Disclosure	0	0
Available-for-sale Securities, Fair Value Disclosure		106,269
Investments held in Rabbi Trust	0	0
Derivative assets	0	0
Assets, Fair Value Disclosure	105,668	106,269
Liabilities Held-In-Trust, Fair Value Disclosure	0	0
Derivative Liability	0	0
Total liabilities	0	0
Fair Value, Inputs, Level 3 [Member] | Pooled Trust Preferred Securities [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	0	875
Fair Value, Inputs, Level 3 [Member] | U.S. Government-Sponsored Agency Securities [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure		0
Fair Value, Inputs, Level 3 [Member] | US States and Political Subdivisions Debt Securities [Member] | Fair Value, Measurements, Recurring [Member]
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
Fair Value, Inputs, Level 3 [Member] | Corporate Debt Securities [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	2,370
Available-for-sale Securities, Fair Value Disclosure		3,275
Fair Value, Inputs, Level 3 [Member] | Collateralized Mortgage Obligations [Member] | Fair Value, Measurements, Recurring [Member]
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
Fair Value, Inputs, Level 3 [Member] | Mortgage-Backed Securities [Member] | Fair Value, Measurements, Recurring [Member]
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
Fair Value, Inputs, Level 3 [Member] | Commercial Mortgage Backed Securities [Member] | Fair Value, Measurements, Recurring [Member]
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
Fair Value, Inputs, Level 3 [Member] | Auction Rate Securities [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	103,298
Available-for-sale Securities, Fair Value Disclosure		102,994
Fair Value, Inputs, Level 3 [Member] | Single-issuer Trust Preferred Securities [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	$ 2,400	$ 2,400