Fair Value Measurements Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Equity securities, value test coverage	95.00%
Fair value price difference threshold	5.00%
Estimated Fair Value	$ 2,497,537	$ 2,080,294
Other real estate owned (OREO)	$ 6,831	10,518
Assumed market return to liquidity	5 years
Weighted average period for recognition of compensation expense	2 years
Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Assumptions used to estimate fair value, prepayment speed	10.50%
Assumptions used to estimate fair value, discount rate	9.50%
Fair Value, Measurements, Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Estimated Fair Value	$ 2,497,537	2,080,294
Total assets	145,595	62,944
Total liabilities	98,859
Fair Value, Measurements, Recurring | Level 1
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Estimated Fair Value	0	0
Total assets	230	392
Total liabilities	22,412
Fair Value, Measurements, Recurring | Level 2
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Estimated Fair Value	2,393,211	1,974,025
Total assets	145,365	62,552
Total liabilities	76,447
Fair Value, Measurements, Recurring | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Estimated Fair Value	104,326	106,269
Total assets	0	0
Total liabilities	0
Fair Value, Measurements, Recurring | Foreign Exchange Contract | Level 1
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total liabilities	199	381
Fair Value, Measurements, Recurring | Foreign Exchange Contract | Level 1
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total assets	230	392
Fair Value, Measurements, Recurring | Forward Commitments | Level 2
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total assets	1,200	1,200
Total liabilities	424	1,100
Fair Value, Measurements, Recurring | Interest Rate Swap | Level 2
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total assets	144,200	61,400
Total liabilities	76,000	47,100
Corporate debt securities
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Estimated Fair Value	377,357
Corporate debt securities | Fair Value, Measurements, Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Estimated Fair Value	377,357	109,533
Corporate debt securities | Fair Value, Measurements, Recurring | Level 1
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Estimated Fair Value	0	0
Corporate debt securities | Fair Value, Measurements, Recurring | Level 2
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Estimated Fair Value	374,957	106,258
Corporate debt securities | Fair Value, Measurements, Recurring | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Estimated Fair Value	2,400	3,275
Financial Institutions Subordinated Debt | Fair Value, Measurements, Recurring | Level 2
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Estimated Fair Value	362,300	86,100
Single-issuer trust preferred securities | Fair Value, Measurements, Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Estimated Fair Value	11,200	18,600
Single-issuer trust preferred securities | Fair Value, Measurements, Recurring | Level 2
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Estimated Fair Value	8,800	16,300
Single-issuer trust preferred securities | Fair Value, Measurements, Recurring | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Estimated Fair Value	2,400
Pooled trust preferred securities | Fair Value, Measurements, Recurring | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Estimated Fair Value	0	875
Other Corporate Debt | Fair Value, Measurements, Recurring | Level 2
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Estimated Fair Value	$ 3,900	$ 3,900