Loans (Activity for Accretable Yield) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield Movement Schedule [Roll Forward]
Balance at beginning of period	$ 926,897	$ 1,039,971	$ 298,257
Addition attributable to acquisitions			862,127
Accretion recognized in interest income	(221,419)	(242,169)	(131,559)
Net reclassification (to) from nonaccretable difference	(58,153)	129,095	11,146
Balance at end of period	647,325	926,897	1,039,971
Talmer
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield Movement Schedule [Roll Forward]
Balance at beginning of period	731,353	798,210	0
Addition attributable to acquisitions			862,127
Accretion recognized in interest income	(164,614)	(175,678)	(63,917)
Net reclassification (to) from nonaccretable difference	(61,407)	108,821	0
Balance at end of period	505,332	731,353	798,210
Lake Michigan
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield Movement Schedule [Roll Forward]
Balance at beginning of period	95,124	121,416	152,999
Addition attributable to acquisitions			0
Accretion recognized in interest income	(24,722)	(29,077)	(33,031)
Net reclassification (to) from nonaccretable difference	2,730	2,785	1,448
Balance at end of period	73,132	95,124	121,416
Monarch
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield Movement Schedule [Roll Forward]
Balance at beginning of period	22,496	27,182	34,558
Addition attributable to acquisitions			0
Accretion recognized in interest income	(3,881)	(4,533)	(5,468)
Net reclassification (to) from nonaccretable difference	(783)	(153)	(1,908)
Balance at end of period	17,832	22,496	27,182
Northwestern
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield Movement Schedule [Roll Forward]
Balance at beginning of period	60,814	69,847	82,623
Addition attributable to acquisitions			0
Accretion recognized in interest income	(17,988)	(20,318)	(15,791)
Net reclassification (to) from nonaccretable difference	(1,371)	11,285	3,015
Balance at end of period	41,455	60,814	69,847
OAK
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield Movement Schedule [Roll Forward]
Balance at beginning of period	17,110	23,316	28,077
Addition attributable to acquisitions			0
Accretion recognized in interest income	(10,214)	(12,563)	(13,352)
Net reclassification (to) from nonaccretable difference	2,678	6,357	8,591
Balance at end of period	$ 9,574	$ 17,110	$ 23,316