Fair Value Measurements Narrative (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities valued by the pricing service	80.00%	80.00%
Researched securities to reconcile the difference	5.00%	5.00%
Corporate debt securities	$ 2,548,457	$ 2,548,457
Significant input, assumed market return to liquidity (years)	5 years
Other real estate owned (OREO)	$ 10,542	$ 10,542	$ 12,815
Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Weighted average annual constant prepayment rate		12.40%
Weighted average discount rate		9.50%
Equity Securities Financial Institution [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, equity securities	12,100	$ 12,100	23,500
Other Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, equity securities	1,000	1,000	1,000
Corporate Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Corporate debt securities	92,977	92,977	109,409
Single-issuer Trust Preferred Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Corporate debt securities	38,251	38,251	39,829
Pooled Trust Preferred Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Corporate debt securities	422	422	422
Fair Value, Measurements, Recurring [Member] | Single-issuer Trust Preferred Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Corporate debt securities	38,300	38,300	39,800
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Trust for Benefit of Employees [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other financial assets	18,100	18,100	16,400
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Foreign Exchange Contract [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other financial assets	625	625	745
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Trust for Benefit of Employees [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other financial liabilities	18,100	18,100	16,400
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Foreign Exchange Contract [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other financial liabilities	506	506	668
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Equity Securities Financial Institution [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, equity securities	12,100	12,100	23,500
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Other Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, equity securities	1,000	1,000	1,000
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Forward Contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other financial assets	1,300	1,300	3,100
Other financial liabilities	223	223	339
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Interest Rate Swap [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other financial assets	47,700	47,700	41,400
Other financial liabilities	41,300	41,300	41,400
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Financial Institutions Subordinated Debt [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Corporate debt securities	50,300	50,300	65,200
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Single-issuer Trust Preferred Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Corporate debt securities	35,500	35,500	37,300
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Other Corporate Debt [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Corporate debt securities	4,000	4,000	4,000
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Single-issuer Trust Preferred Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Corporate debt securities	2,800	2,800	2,500
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Pooled Trust Preferred Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Corporate debt securities	422	422	422
Fair Value, Measurements, Nonrecurring [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other real estate owned (OREO)	10,542	10,542	12,815
Net MSRs at end of period	$ 37,874	$ 37,874	$ 37,532