Acquisitions (Activity for Acquired Loans) (Details) - USD ($) $ in Thousands					9 Months Ended
		May. 31, 2015	Apr. 01, 2015	Oct. 31, 2014	Sep. 30, 2015	Sep. 30, 2014
Activity for accretable yield includes contractually due interest of acquired loans
Balance at beginning of period					$ 137,961
Additions attributable to acquisitions					228,160
Accretable Yield Additions, Net of Reductions	[1]				1,532
Accretion recognized in interest income					(40,828)
Reclassification from nonaccretable difference					0
Balance at end of period					326,825
Northwestern Bancorp [Member]
Activity for accretable yield includes contractually due interest of acquired loans
Balance at beginning of period					104,675
Additions attributable to acquisitions				$ 110,000	0
Accretable Yield Additions, Net of Reductions	[1]				(4,196)
Accretion recognized in interest income					(14,434)
Reclassification from nonaccretable difference					0
Balance at end of period					86,045
OAK [Member]
Activity for accretable yield includes contractually due interest of acquired loans
Balance at beginning of period					33,286	$ 32,610
Additions attributable to acquisitions					0	0
Accretable Yield Additions, Net of Reductions	[1]				6,417	4,493
Accretion recognized in interest income					(9,151)	(11,262)
Reclassification from nonaccretable difference					0	10,000
Balance at end of period					30,552	$ 37,349
Lake Michigan Financial Corp [Member]
Activity for accretable yield includes contractually due interest of acquired loans
Balance at beginning of period					0
Additions attributable to acquisitions		$ 190,200			190,246
Accretable Yield Additions, Net of Reductions	[1]				803
Accretion recognized in interest income					(14,190)
Reclassification from nonaccretable difference					0
Balance at end of period					176,859
Monarch Community Bancorp [Member]
Activity for accretable yield includes contractually due interest of acquired loans
Balance at beginning of period					0
Additions attributable to acquisitions			$ 37,900		37,914
Accretable Yield Additions, Net of Reductions	[1]				(1,492)
Accretion recognized in interest income					(3,053)
Reclassification from nonaccretable difference					0
Balance at end of period					$ 33,369

[1] Represents additions of estimated contractual interest expected to be collected from acquired loans being renewed or extended, less reductions in contractual interest resulting from the early payoff of acquired loans.