Acquisitions (Activity for Acquired Loans) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015		Mar. 31, 2014
Activity for accretable yield includes contractually due interest of acquired loans
Balance at beginning of period	$ 137,961
Accretable Yield Additions, Net of Reductions	(696)	[1]
Accretion recognized in interest income	(8,205)
Reclassification from nonaccretable difference	0
Balance at end of period	129,060
Northwestern Bancorp [Member]
Activity for accretable yield includes contractually due interest of acquired loans
Balance at beginning of period	104,675
Accretable Yield Additions, Net of Reductions	(1,410)	[1]
Accretion recognized in interest income	(4,998)
Reclassification from nonaccretable difference	0
Balance at end of period	98,267
OAK [Member]
Activity for accretable yield includes contractually due interest of acquired loans
Balance at beginning of period	33,286		32,610
Accretable Yield Additions, Net of Reductions	714	[1]	821	[1]
Accretion recognized in interest income	(3,207)		(3,843)
Reclassification from nonaccretable difference	0		10,000
Balance at end of period	$ 30,793		$ 39,588

[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.