Mergers and Acquisitions (Assets Acquired and Liabilities Assumed) (Details) - USD ($) $ in Thousands	Aug. 31, 2016	Dec. 31, 2018	Dec. 31, 2017
Fair value of liabilities assumed:
Goodwill resulting from acquisition		$ 1,134,568	$ 1,134,568
Talmer
Consideration paid:
Stock	$ 1,504,811
Cash	107,638
Total consideration	1,612,449
Fair value of identifiable assets acquired:
Cash and cash equivalents	433,352
Investment securities:
Available-for-sale	808,894
Held-to-maturity	1,657
Loans held-for-sale	244,916
Loans	4,882,402
Premises and equipment	38,793
Loan servicing rights	42,462
Other intangible assets	19,088
Interest receivable and other assets	395,539
Total identifiable assets acquired	6,867,103
Fair value of liabilities assumed:
Noninterest-bearing deposits	1,236,902
Interest-bearing deposits	4,057,716
Interest payable and other liabilities	100,936
Securities sold under agreements to repurchase with customers	19,704
Short-term borrowings	387,500
Long-term borrowings	299,597
Total liabilities assumed	6,102,355
Fair value of net identifiable assets acquired	764,748
Goodwill resulting from acquisition	$ 847,701