Acquisitions (Activity for Acquired Loans) (Details) - USD ($) $ in Thousands					6 Months Ended
		May 31, 2015	Apr. 01, 2015	Oct. 31, 2014	Jun. 30, 2016	Jun. 30, 2015
Activity for accretable yield includes contractually due interest of acquired loans
Balance at beginning of period					$ 298,257	$ 137,961
Additions attributable to acquisitions						228,160
Additions (reductions)	[1]				(17,277)	2,765
Accretion recognized in interest income					(34,440)	(20,838)
Reclassification from nonaccretable difference					10,000
Balance at end of period					256,540	348,048
Northwestern Bancorp [Member]
Activity for accretable yield includes contractually due interest of acquired loans
Balance at beginning of period					82,623	104,675
Additions attributable to acquisitions				$ 110,000		0
Additions (reductions)	[1]				(5,848)	(2,859)
Accretion recognized in interest income					(8,029)	(10,058)
Reclassification from nonaccretable difference					5,000
Balance at end of period					73,746	91,758
OAK [Member]
Activity for accretable yield includes contractually due interest of acquired loans
Balance at beginning of period					28,077	33,286
Additions attributable to acquisitions						0
Additions (reductions)	[1]				(201)	5,215
Accretion recognized in interest income					(6,284)	(6,326)
Reclassification from nonaccretable difference					5,000
Balance at end of period					26,592	32,175
Lake Michigan Financial Corp [Member]
Activity for accretable yield includes contractually due interest of acquired loans
Balance at beginning of period					152,999	0
Additions attributable to acquisitions		$ 190,200				190,246
Additions (reductions)	[1]				(10,365)	1,550
Accretion recognized in interest income					(17,291)	(3,486)
Reclassification from nonaccretable difference					0
Balance at end of period					125,343	188,310
Monarch Community Bancorp [Member]
Activity for accretable yield includes contractually due interest of acquired loans
Balance at beginning of period					34,558	0
Additions attributable to acquisitions			$ 37,900			37,914
Additions (reductions)	[1]				(863)	(1,141)
Accretion recognized in interest income					(2,836)	(968)
Reclassification from nonaccretable difference					0
Balance at end of period					$ 30,859	$ 35,805

[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.