Loans - Activity for Accretable Yield (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Activity for accretable yield
Balance at beginning of period	$ 868,698	$ 1,000,408	$ 926,897	$ 1,039,971
Accretion recognized in interest income	(56,900)	(62,614)	(115,461)	(122,801)
Net reclassification (to) from nonaccretable difference	(31,034)	100,425	(30,672)	121,049
Balance at end of period	780,764	1,038,219	780,764	1,038,219
Talmer
Activity for accretable yield
Balance at beginning of period	685,830	774,778	731,353	798,210
Accretion recognized in interest income	(42,136)	(45,091)	(84,776)	(89,662)
Net reclassification (to) from nonaccretable difference	(27,526)	71,682	(30,409)	92,821
Balance at end of period	616,168	801,369	616,168	801,369
Lake Michigan
Activity for accretable yield
Balance at beginning of period	90,156	113,211	95,124	121,416
Accretion recognized in interest income	(6,302)	(7,583)	(13,060)	(14,849)
Net reclassification (to) from nonaccretable difference	(3,412)	15,944	(1,622)	15,005
Balance at end of period	80,442	121,572	80,442	121,572
Monarch
Activity for accretable yield
Balance at beginning of period	21,154	26,055	22,496	27,182
Accretion recognized in interest income	(962)	(1,159)	(2,118)	(2,340)
Net reclassification (to) from nonaccretable difference	(61)	(626)	(247)	(572)
Balance at end of period	20,131	24,270	20,131	24,270
North-western
Activity for accretable yield
Balance at beginning of period	55,400	64,897	60,814	69,847
Accretion recognized in interest income	(4,618)	(5,467)	(9,522)	(9,359)
Net reclassification (to) from nonaccretable difference	(1,051)	11,782	(1,561)	10,724
Balance at end of period	49,731	71,212	49,731	71,212
OAK
Activity for accretable yield
Balance at beginning of period	16,158	21,467	17,110	23,316
Accretion recognized in interest income	(2,882)	(3,314)	(5,985)	(6,591)
Net reclassification (to) from nonaccretable difference	1,016	1,643	3,167	3,071
Balance at end of period	$ 14,292	$ 19,796	$ 14,292	$ 19,796

The aggregate excess of a loan's cash flows expected to be collected over the investor's initial investment in the loan for loans accounted for as debt securities, with evidence of deterioration of credit quality since origination that were acquired by completion of a transfer for which it is probable, at acquisition, that the investor will be unable to collect all contractually required payments receivable.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 30
-Section 15
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=82894507&loc=d3e13503-111538

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 30
-Section 50
-Paragraph 2
-Subparagraph (a)(2)
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- Definition

Current period recognition due to accretion of the excess of a loan's cash flows expected to be collected over the investor's initial investment in the loan for loans accounted for as debt securities, with evidence of deterioration of credit quality since origination that were acquired by completion of a transfer for which it is probable, at acquisition, that the investor will be unable to collect all contractually required payments receivable.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 30
-Section 50
-Paragraph 2
-Subparagraph (a)(2)
-URI http://asc.fasb.org/extlink&oid=82894903&loc=d3e15032-111544

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 30
-Section 15
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=82894507&loc=d3e13503-111538

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- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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No definition available.

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- Definition

Change in the estimate of cash flows expected to be collected, after acquisition of a loan, which results in an increase in accretable yield (for example, if actual cash flows are significantly greater than previously expected). This relates to loans accounted for as debt securities, with evidence of deterioration of credit quality since origination that was acquired by completion of a transfer for which it is probable, at acquisition, that the investor will be unable to collect all contractually required payments receivable.

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