Investment Securities (Narrative) (Details) $ in Thousands			6 Months Ended	12 Months Ended
	Mar. 31, 2016 USD ($) Securities yr	Dec. 31, 2015 USD ($) Securities	Jun. 30, 2015 USD ($)	Dec. 31, 2015 USD ($) Securities
Investment [Line Items]
Sale of CDO, Amortized Cost			$ 574,000
Held-to-maturity, Amortized cost	$ 631,646
Private equity investments prohibited by Volker rule	$ 16,000
Number of HTM investment securities in an unrealized loss position | Securities	157	187		187
Number of AFS investment securities in an unrealized loss position | Securities	684	709		709
Carrying value of pledged securities	$ 2,000,000	$ 2,300,000		$ 2,300,000
Private Equity Investments	134,000
Realized Losses on Sales of CDOs			(137,000)
Private Equity Investments Sold Prohibited by Volcker Rule				9,000
Commitments for Private Equity and Other Noninterest-bearing Investments	20,000
Commitments for Private Equity or Other Non-Interest Bearing Investments Prohibited by the Volcker Rule	$ 6,000
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	$ 631,646	545,648		$ 545,648
Held To Maturity Securities Gross Unrealized Losses	$ 6,681	$ 4,778
Asset-backed Securities [Member] | Trust Preferred Securities - Banks And Insurance [Member]
Investment [Line Items]
Held-to-maturity, Amortized cost			$ 79,000