Loans and Leases (Details Textual)	12 Months Ended
	Dec. 31, 2015 USD ($) Contract	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Financing Receivable, Impaired [Line Items]
Unfunded Commitments For Troubled Debt Restructurings	$ 2,900,000	$ 214,000
Financing Receivable, Recorded Investment, Nonaccrual Status	129,019,000	83,621,000
Loan Receivable, Recorded Investment, Equal to Greater than 90 Days Past Due	16,800,000
Loans and Leases Receivable, Gross	14,528,165,000	11,904,684,000
Financing Receivables, Impaired, Troubled Debt Restructuring, Write-down	96,900	129,000	$ 1,600,000
Financing Receivable Recorded Investment Thirty to Eighty Nine Days Past Due	3,600,000	8,700,000
Financing Receivable Recorded Investment Nonaccrual Status Current	108,600,000	56,100,000
Loans and Leases Receivable, Impaired, Interest Lost on Nonaccrual Loans	6,400,000	7,500,000
Non Purchased Credit Impaired Loans and Leases [Member]
Financing Receivable, Impaired [Line Items]
Financing Receivable, Recorded Investment, Nonaccrual Status	129,019,000	83,621,000
Loan Receivable, Recorded Investment, Equal to Greater than 90 Days Past Due	17,508,000	18,818,000
Loans held for investment, net	14,289,209,000	11,591,641,000
Loans and Leases Receivable, Gross	14,339,070,000	11,613,832,000
Financing Receivable Recorded Investment Thirty to Eighty Nine Days Past Due	10,622,000	19,406,000
Purchased Credit Impaired Loans and Leases [Member]
Financing Receivable, Impaired [Line Items]
Loans held for investment, net	189,045,000	290,791,000
Loans and Leases Receivable, Gross	$ 189,095,000	$ 290,852,000
Nonperforming Financing Receivable [Member] | Oil and Gas Properties [Member]
Financing Receivable, Impaired [Line Items]
Financing Receivable, Number Of Contracts | Contract	3
Loans held for investment, net	$ 47,100,000