Other Intangible Assets (Textual) (Details) (USD $)	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012		Oct. 31, 2014	Dec. 07, 2012
Finite-Lived Intangible Assets [Line Items]
Loans serviced for others that have servicing rights capitalized	2,093,140,000		886,730,000
Estimated Future Amortization Expense, Fiscal Year Maturity [Abstract]
Impairment valuation allowance	200,000	[1]	0	[1]	0	[1]
Core deposit intangible assets [Member]
Estimated Future Amortization Expense, Fiscal Year Maturity [Abstract]
2015	3,200,000
2016	2,900,000
2017	2,600,000
2018	2,500,000
2019	2,400,000
Thereafter	7,300,000
Northwestern Bancorp [Member]
Estimated Future Amortization Expense, Fiscal Year Maturity [Abstract]
Intangibles acquired							12,891,000
Independent Bank [Member]
Estimated Future Amortization Expense, Fiscal Year Maturity [Abstract]
Intangibles acquired								5,600,000
Independent Bank [Member] | Core deposit intangible assets [Member]
Estimated Future Amortization Expense, Fiscal Year Maturity [Abstract]
Intangibles acquired								5,600,000
Originated Portfolio Segment [Member]
Finite-Lived Intangible Assets [Line Items]
Loans serviced for others that have servicing rights capitalized	881,000,000
Originated Portfolio Segment [Member] | Weighted Average [Member] | Mortgage servicing rights [Member]
Estimated Future Amortization Expense, Fiscal Year Maturity [Abstract]
Coupon rate (percent)	4.28%		4.33%
Discount rate (percent)	8.50%		8.50%
Prepayment speed rate (percent)	13.60%		11.30%
Acquired Portfolio Segment [Member]
Finite-Lived Intangible Assets [Line Items]
Loans serviced for others that have servicing rights capitalized	1,210,000,000
Acquired Portfolio Segment [Member] | Weighted Average [Member] | Mortgage servicing rights [Member]
Estimated Future Amortization Expense, Fiscal Year Maturity [Abstract]
Coupon rate (percent)	4.08%
Discount rate (percent)	10.10%
Prepayment speed rate (percent)	11.65%

[1] MSRs are stratified into servicing assets originated by the Corporation and those acquired in acquisitions of other institutions and further stratified into relatively homogeneous pools based on products with similar characteristics. The MSR impairment valuation allowance recorded at December 31, 2014 related to impairment within certain pools attributable to the Corporation's servicing portfolio that was acquired in the Northwestern transaction.