Investment Securities Narrative (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2016 USD ($) Security	Dec. 31, 2015 USD ($)
Schedule of Investments [Line Items]
Available-for-sale Securities Pledged as Collateral	$ 1,700,000	$ 1,674,687
Amortized cost	2,494,087	2,494,059
Available-for-sale Securities, Fair Value Disclosure	2,529,724	2,484,773
Single Bank Stock Investment, cost basis	7,400
Single Bank Stock Investment, Fair Value	$ 10,400
Percent Ownership In An Individual Financial Institution	52.50%
Individual Bank Stock Investment Percent to Total Portfolio	10.00%
Auction Rate Certificates Not Subject To Any Additional Other Than Temporary Impairment Charges Fair Value	$ 97,900
Domestic Corporate debt securities	91,500
Equity Securities [Member]
Schedule of Investments [Line Items]
Amortized cost	14,210	14,677
Available-for-sale Securities, Fair Value Disclosure	20,689	21,514
Equity Securities Financial Institution [Member]
Schedule of Investments [Line Items]
Available-for-sale Securities, Equity Securities	19,800	$ 20,600
Amortized cost	13,400
Available-for-sale Securities, Fair Value Disclosure	19,800
Equity Securities, Other [Member]
Schedule of Investments [Line Items]
Available-for-sale Securities, Equity Securities	895
Single-issuer Trust Preferred Securities [Member]
Schedule of Investments [Line Items]
Unrealized Loss on Securities	$ 6,200
Number of Trust Preferred Securities | Security	19
External Credit Rating, BBB [Member] | Single-issuer Trust Preferred Securities [Member]
Schedule of Investments [Line Items]
Amortized cost	$ 3,700
Available-for-sale Securities, Fair Value Disclosure	2,400
External Credit Rating, Rated Below Investment Grade [Member] | Single-issuer Trust Preferred Securities [Member]
Schedule of Investments [Line Items]
Amortized cost	11,500
Available-for-sale Securities, Fair Value Disclosure	$ 9,500
Number of Trust Preferred Securities | Security	6