Loans and Leases (Details 6) $ in Thousands	Sep. 30, 2015 USD ($) Contract	Jun. 30, 2015 USD ($) Contract	Dec. 31, 2014 USD ($)	Sep. 30, 2014 USD ($)
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	$ 12,452,205		$ 11,882,432
NonCovered [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	12,258,916		11,591,641	$ 11,223,506
Oil and Gas Properties [Member] | Lease Agreements [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	$ 69,247	$ 90,189
Financing Receivable, Number Of Contracts | Contract	20	21
Oil and Gas Properties [Member] | Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	$ 83,025	$ 87,005
Financing Receivable, Number Of Contracts | Contract	7	8
Oil and Gas Properties [Member] | Loans and Leases [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	$ 152,272	$ 177,194
Financing Receivable, Number Of Contracts | Contract	27	29
Classified [Member] | NonCovered [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	$ 328,038		$ 242,611
Classified [Member] | Oil and Gas Properties [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	$ 47,853	$ 64,232
Financing Receivable, Number Of Contracts | Contract	4	4
Nonperforming Financing Receivable [Member] | Oil and Gas Properties [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	$ 47,853	$ 64,232
Financing Receivable, Number Of Contracts | Contract	4	4