Loans - Activity for Accretable Yield (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Activity for accretable yield
Balance at beginning of period	$ 647,325	$ 926,897
Accretion recognized in interest income	(49,145)	(58,561)
Net reclassification (to) from nonaccretable difference	4,484	362
Balance at end of period	602,664	868,698
Talmer
Activity for accretable yield
Balance at beginning of period	505,332	731,353
Accretion recognized in interest income	(38,031)	(42,640)
Net reclassification (to) from nonaccretable difference	2,412	(2,883)
Balance at end of period	469,713	685,830
Lake Michigan
Activity for accretable yield
Balance at beginning of period	73,132	95,124
Accretion recognized in interest income	(5,551)	(6,758)
Net reclassification (to) from nonaccretable difference	1,414	1,790
Balance at end of period	68,995	90,156
Monarch
Activity for accretable yield
Balance at beginning of period	17,832	22,496
Accretion recognized in interest income	(774)	(1,156)
Net reclassification (to) from nonaccretable difference	(91)	(186)
Balance at end of period	16,967	21,154
North-western
Activity for accretable yield
Balance at beginning of period	41,455	60,814
Accretion recognized in interest income	(3,420)	(4,904)
Net reclassification (to) from nonaccretable difference	609	(510)
Balance at end of period	38,644	55,400
OAK
Activity for accretable yield
Balance at beginning of period	9,574	17,110
Accretion recognized in interest income	(1,369)	(3,103)
Net reclassification (to) from nonaccretable difference	140	2,151
Balance at end of period	$ 8,345	$ 16,158