Fair Value Measurements Narrative (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2019	Dec. 31, 2018
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Securities valued by the pricing service	95.00%
Researched securities to reconcile the difference	5.00%
Available for sale, at estimated fair value	$ 2,159,806	$ 2,080,294
Significant input, assumed market return to liquidity (years)	5 years
Other real estate owned (OREO)	$ 9,012	10,518
Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Weighted average annual constant prepayment rate	9.50%
Weighted average discount rate	9.00%
Fair Value, Measurements, Recurring [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Available for sale, at estimated fair value	$ 2,159,806
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Available for sale, at estimated fair value	0
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Available for sale, at estimated fair value	2,053,796
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 3 [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Available for sale, at estimated fair value	106,010
Fair Value, Measurements, Recurring [Member] \| Financial Institutions Subordinated Debt [Member] \| Fair Value, Inputs, Level 2 [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Available for sale, at estimated fair value	97,200	86,100
Fair Value, Measurements, Recurring [Member] \| Single-issuer Trust Preferred Securities [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Available for sale, at estimated fair value	19,300	18,600
Fair Value, Measurements, Recurring [Member] \| Single-issuer Trust Preferred Securities [Member] \| Fair Value, Inputs, Level 2 [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Available for sale, at estimated fair value	17,000	16,300
Fair Value, Measurements, Recurring [Member] \| Single-issuer Trust Preferred Securities [Member] \| Fair Value, Inputs, Level 3 [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Available for sale, at estimated fair value	2,400
Fair Value, Measurements, Recurring [Member] \| Pooled Trust Preferred Securities [Member] \| Fair Value, Inputs, Level 3 [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Available for sale, at estimated fair value	770	875
Fair Value, Measurements, Recurring [Member] \| Other Corporate Debt [Member] \| Fair Value, Inputs, Level 2 [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Available for sale, at estimated fair value	3,900
Fair Value, Measurements, Recurring [Member] \| Trust for Benefit of Employees [Member] \| Fair Value, Inputs, Level 1 [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other financial liabilities	20,000	18,400
Fair Value, Measurements, Recurring [Member] \| Foreign Exchange Contract [Member] \| Fair Value, Inputs, Level 1 [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other financial liabilities	356	381
Fair Value, Measurements, Nonrecurring [Member] \| Fair Value, Inputs, Level 3 [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other real estate owned (OREO)	9,012	10,518
Net MSRs at end of period	38,504	38,573
Foreign Exchange Contract [Member] \| Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other financial assets	415	392
Forward Commitments [Member] \| Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other financial assets	1,800	1,200
Other financial liabilities	1,100
Interest Rate Swap [Member] \| Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other financial assets	79,900	61,400
Other financial liabilities	$ 49,000	$ 47,100

Differences by security in excess of of threhold are researched to reconcile the difference.

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Carrying amount as of the balance sheet date of other real estate and foreclosed assets. Other real estate may include real estate investments, real estate loans that qualify as investments in real estate, and premises that are no longer used in operations may also be included in real estate owned. Foreclosed assets include all assets obtained in full or partial satisfaction of a debt arrangement through foreclosure proceedings.

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Fair value of contract to service financial assets under which the benefits of servicing are expected to more than adequately compensate the servicer.

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