Investment Securities Narrative (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2017 USD ($) Security	Dec. 31, 2016 USD ($)	Jun. 30, 2016 USD ($)
Schedule of Investments [Line Items]
Securities pledged as collateral	$ 1,700,000	$ 1,800,000
Amortized cost	2,503,895	2,594,255
Available-for-sale Securities, Fair Value Disclosure	2,488,699	2,559,227
Single Bank Stock Investment, cost basis	4,300
Single Bank Stock Investment, Fair Value	$ 8,800
Percent Ownership In An Individual Financial Institution	42.90%
Individual Bank Stock Investment Percent to Total Portfolio	10.00%
Equity Securities [Member]
Schedule of Investments [Line Items]
Amortized cost	$ 10,487	12,231
Available-for-sale Securities, Fair Value Disclosure	21,455	24,526
Equity Securities Financial Institution [Member]
Schedule of Investments [Line Items]
Available-for-sale Securities, Equity Securities	20,500	23,500
Amortized cost	9,700
Available-for-sale Securities, Fair Value Disclosure	20,500
Other Equity Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Securities, Equity Securities	1,000	$ 1,000
Single-issuer Trust Preferred Securities [Member]
Schedule of Investments [Line Items]
Unrealized Loss on Securities	$ 1,300
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	$ 3,800
Available-for-sale Securities, Fair Value Disclosure	2,800
External Credit Rating, Rated Below Investment Grade [Member] | Single-issuer Trust Preferred Securities [Member]
Schedule of Investments [Line Items]
Amortized cost	11,600
Available-for-sale Securities, Fair Value Disclosure	$ 10,900
Number of Trust Preferred Securities | Security	6
Pooled Trust Preferred Securities [Member]
Schedule of Investments [Line Items]
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Credit Losses on Debt Securities Held	$ 10,000		$ 10,000