Fair Value Measurements Fair Value Measurements, Financial Instruments Measured On a Recurring Basis, Quantitative Information (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Available for sale securities	$ 8,857,120	$ 8,321,578
Municipal and other tax-exempt securities [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Available for sale securities	2,864	27,080
Other debt securities [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Available for sale securities	35,430	25,481
Fair Value, Measurements, Recurring [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Available for sale securities	8,857,120	8,321,578
Residential mortgage loans held for sale	149,221	221,378
Fair Value, Measurements, Recurring [Member] | Municipal and other tax-exempt securities [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Available for sale securities	2,864	27,080
Fair Value, Measurements, Recurring [Member] | Other debt securities [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Available for sale securities	35,430	25,481
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Available for sale securities	472	5,274
Residential mortgage loans held for sale	15,207	12,299
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Municipal and other tax-exempt securities [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Available for sale securities		4,802
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Other debt securities [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Available for sale securities	$ 472	$ 472
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Available for sale securities [Member] | Municipal and other tax-exempt securities [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment Grade Tax Exempt Securities Yield Spread Over Comparable Securities, Minimum		372
Investment Grade Tax Exempt Securities Yield Spread Over Comparable Securities, Maximum		466
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Available for sale securities [Member] | Other debt securities [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Average Yields On Comparable Short-term Taxable Securities	3.00%	3.00%
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Residential mortgage loans held for sale [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Liquidity Discount on Mortgage Loans Qualifying for Sale to US Govt Agencies	92.38%	94.75%
Discounted Cash Flow [Member] | Interest Rate Spread [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Available for sale securities [Member] | Municipal and other tax-exempt securities [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Available for sale securities		$ 4,802
Discounted Cash Flow [Member] | Interest Rate Spread [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Available for sale securities [Member] | Other debt securities [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Available for sale securities	$ 472	472
Quoted prices of loans sold in securitization transactions, with a liquidity discount applied [Member] | Liquidity discount [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Residential mortgage loans held for sale [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Residential mortgage loans held for sale	$ 15,207	$ 12,299
Minimum [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Available for sale securities [Member] | Municipal and other tax-exempt securities [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Range of fair value as a percentage of par value	0.00%	92.25%
Range of interest rates used to value securities	0.00%	6.60%
Minimum [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Available for sale securities [Member] | Other debt securities [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Range of fair value as a percentage of par value	94.44%	94.39%
Range of interest rates used to value securities	7.88%	6.85%
Maximum [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Available for sale securities [Member] | Municipal and other tax-exempt securities [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Range of fair value as a percentage of par value	0.00%	94.76%
Range of interest rates used to value securities	0.00%	6.60%
Maximum [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Available for sale securities [Member] | Other debt securities [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Range of fair value as a percentage of par value	94.44%	94.39%
Range of interest rates used to value securities	7.88%	6.85%
Weighted Average [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Available for sale securities [Member] | Municipal and other tax-exempt securities [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Range of fair value as a percentage of par value	0.00%	93.75%
Range of interest rates used to value securities	0.00%	6.60%
Weighted Average [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Available for sale securities [Member] | Other debt securities [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Range of fair value as a percentage of par value	94.44%	94.39%
Range of interest rates used to value securities	7.88%	6.85%