Investment Securities (Narrative) (Details) $ in Thousands			6 Months Ended	9 Months Ended		12 Months Ended
	Sep. 30, 2015 USD ($) Securities yr	Dec. 31, 2014 USD ($) Securities	Jun. 30, 2015 USD ($)	Sep. 30, 2015 USD ($) Securities	Sep. 30, 2014 USD ($)	Dec. 31, 2014 USD ($) Securities	Mar. 31, 2015 USD ($)
Investment [Line Items]
Sale of CDO, Amortized Cost			$ 574,000
Held-to-maturity, Amortized cost	$ 544,168	$ 686,951		$ 544,168		$ 686,951
Private equity investments prohibited by Volker rule	$ 24,000			$ 24,000
Number of HTM investment securities in an unrealized loss position | Securities	146	153		146		153
Number of AFS investment securities in an unrealized loss position | Securities	460	458		460		458
Carrying value of pledged securities	$ 1,900,000	$ 1,400,000		$ 1,900,000		$ 1,400,000
Private Equity Investments	140,000			140,000
Par Value of CDO Securities Sold					$ 1,294,000
Realized Losses on Sales of CDOs			(137,000)
Held To Maturity Securities Gross Unrealized Losses		39,699
Private Equity Investments Sold Prohibited by Volcker Rule			$ 9,000	17,000	$ 22,000	8,000
Commitments for Private Equity and Other Noninterest-bearing Investments	48,000			48,000
Commitments for Private Equity or Other Non-Interest Bearing Investments Prohibited by the Volcker Rule	$ 8,000			8,000
Small Business Administration Loan-Backed Securities [Member] | Minimum [Member]
Investment [Line Items]
Investment term of maturity | yr	5
Small Business Administration Loan-Backed Securities [Member] | Maximum [Member]
Investment [Line Items]
Investment term of maturity | yr	25
Municipal Securities [Member]
Investment [Line Items]
Held-to-maturity, Amortized cost	$ 544,168	607,675		$ 544,168		$ 607,675
Held To Maturity Securities Gross Unrealized Losses		0
Asset-backed Securities [Member] | Trust Preferred Securities - Banks And Insurance [Member]
Investment [Line Items]
Held-to-maturity, Amortized cost							$ 79,276
Held To Maturity Securities Gross Unrealized Losses		$ 39,699