Loans - Activity for Accretable Yield (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Activity for accretable yield
Balance at beginning of period	$ 1,000,408	$ 274,614	$ 1,039,971	$ 298,257
Accretion recognized in interest income	(62,614)	(17,478)	(122,801)	(34,440)
Net reclassification (to) from nonaccretable difference	100,425	(596)	121,049	(7,277)
Balance at end of period	1,038,219	256,540	1,038,219	256,540
Talmer
Activity for accretable yield
Balance at beginning of period	774,778	0	798,210	0
Accretion recognized in interest income	(45,091)	0	(89,662)	0
Net reclassification (to) from nonaccretable difference	71,682	0	92,821	0
Balance at end of period	801,369	0	801,369	0
Lake Michigan
Activity for accretable yield
Balance at beginning of period	113,211	137,975	121,416	152,999
Accretion recognized in interest income	(7,583)	(8,338)	(14,849)	(17,291)
Net reclassification (to) from nonaccretable difference	15,944	(4,294)	15,005	(10,365)
Balance at end of period	121,572	125,343	121,572	125,343
Monarch
Activity for accretable yield
Balance at beginning of period	26,055	33,235	27,182	34,558
Accretion recognized in interest income	(1,159)	(1,385)	(2,340)	(2,836)
Net reclassification (to) from nonaccretable difference	(626)	(991)	(572)	(863)
Balance at end of period	24,270	30,859	24,270	30,859
North-western
Activity for accretable yield
Balance at beginning of period	64,897	76,368	69,847	82,623
Accretion recognized in interest income	(5,467)	(4,028)	(9,359)	(8,029)
Net reclassification (to) from nonaccretable difference	11,782	1,406	10,724	(848)
Balance at end of period	71,212	73,746	71,212	73,746
OAK
Activity for accretable yield
Balance at beginning of period	21,467	27,036	23,316	28,077
Accretion recognized in interest income	(3,314)	(3,727)	(6,591)	(6,284)
Net reclassification (to) from nonaccretable difference	1,643	3,283	3,071	4,799
Balance at end of period	$ 19,796	$ 26,592	$ 19,796	$ 26,592