Acquisitions (Textual) (Details) (USD $)	6 Months Ended			3 Months Ended	6 Months Ended		0 Months Ended		0 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Dec. 31, 2013	Jun. 30, 2014 Northwestern Bancorp, Inc. [Member]	Jun. 30, 2014 Northwestern Bancorp, Inc. [Member]	Mar. 10, 2014 Northwestern Bancorp, Inc. [Member]	Dec. 07, 2012 Independent Bank [Member] Branches	Dec. 07, 2012 Independent Bank [Member] Core Deposits [Member]	Apr. 30, 2010 OAK [Member] Offices	Jun. 30, 2014 OAK [Member]	Dec. 31, 2013 OAK [Member]	Jun. 30, 2013 OAK [Member]
Business Acquisition [Line Items]
Estimated purchase price for pending acquisition of Northwestern Bancorp, Inc.						$ 120,000,000
Business Acquisition, Transaction Costs				700,000	1,000,000
Number of branches acquired (branches)							21
Deposits acquired							404,000,000
Loans acquired							44,000,000		627,000,000
Acquisition purchase price							8,100,000		83,700,000
Premium paid on deposits purchased							11,500,000
Premium paid as a percentage of deposits purchased (percent)							2.85%
Discount on loans purchased (percent)							1.75%
Goodwill	120,164,000	120,164,000	120,164,000				6,800,000
Intangibles acquired								5,600,000
Service provided by acquiree bank through number of branches									14
Assets of acquiree company									820,000,000
Deposits of acquiree company									693,000,000
Brokered deposits of acquiree company									193,000,000
Contractually required principal payments of loan portfolio, acquisition date									683,000,000
Acquired loan portfolio acquisition date fair value									627,000,000
Outstanding contractual principal balance of acquired loan portfolio										298,000,000	320,000,000	370,000,000
Carrying amount of acquired loan portfolio										274,000,000	295,000,000	345,000,000
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield, Reclassifications from Nonaccretable Difference	$ 10,000,000	$ 125,000