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Acquisitions - Schedule of Recognized Identifiable Assets Acquired and Liabilities Assumed (Details) - USD ($) $ in Millions | Apr. 08, 2019 | Aug. 16, 2018 | Jun. 30, 2019 | Dec. 31, 2018 | Dec. 31, 2017
--- | --- | --- | --- | --- | ---
Liabilities assumed: |  |  |  |  |
Goodwill |  |  | $ 623.5 | $ 546.7 | $ 444.7
Idaho Independent Bank, As Recorded By Idaho Independent Bank |  |  |  |  |
Assets acquired: |  |  |  |  |
Cash and cash equivalents | $ 270.7 |  |  |  |
Investment securities | 62.7 |  |  |  |
Loans held for investment | 347.6 |  |  |  |
Mortgage loans held for sale | 0.5 |  |  |  |
Allowance for loan loss | (6.3) |  |  |  |
Premises and equipment | 16.5 |  |  |  |
Other real estate owned (“OREO”) | 0.4 |  |  |  |
Company owned life insurance | 15.2 |  |  |  |
Core deposit intangible assets | 0.0 |  |  |  |
Deferred tax assets, net | 3.2 |  |  |  |
Other assets | 8.6 |  |  |  |
Total assets acquired | 719.1 |  |  |  |
Liabilities assumed: |  |  |  |  |
Deposits | 596.5 |  |  |  |
Accounts payable and accrued expense | 15.2 |  |  |  |
Other borrowed funds | 4.0 |  |  |  |
Securities sold under repurchase agreements | 30.4 |  |  |  |
Total liabilities assumed | 646.1 |  |  |  |
Net assets acquired | 73.0 |  |  |  |
Idaho Independent Bank, Fair Value Adjustments |  |  |  |  |
Assets acquired: |  |  |  |  |
Cash and cash equivalents | 0.0 |  |  |  |
Investment securities | 0.5 |  |  |  |
Loans held for investment | (9.8) |  |  |  |
Mortgage loans held for sale | 0.0 |  |  |  |
Allowance for loan loss | 6.3 |  |  |  |
Premises and equipment | 3.8 |  |  |  |
Other real estate owned (“OREO”) | 2.0 |  |  |  |
Company owned life insurance | 0.0 |  |  |  |
Core deposit intangible assets | 13.6 |  |  |  |
Deferred tax assets, net | (3.0) |  |  |  |
Other assets | (0.8) |  |  |  |
Total assets acquired | 12.6 |  |  |  |
Liabilities assumed: |  |  |  |  |
Deposits | 0.1 |  |  |  |
Accounts payable and accrued expense | 2.8 |  |  |  |
Other borrowed funds | 0.1 |  |  |  |
Securities sold under repurchase agreements | 0.0 |  |  |  |
Total liabilities assumed | 3.0 |  |  |  |
Net assets acquired | 9.6 |  |  |  |
Idaho Independent Bank |  |  |  |  |
Assets acquired: |  |  |  |  |
Cash and cash equivalents | 270.7 |  |  |  |
Investment securities | 63.2 |  |  |  |
Loans held for investment | 337.8 |  |  |  |
Mortgage loans held for sale | 0.5 |  |  |  |
Allowance for loan loss | 0.0 |  |  |  |
Premises and equipment | 20.3 |  |  |  |
Other real estate owned (“OREO”) | 2.4 |  |  |  |
Company owned life insurance | 15.2 |  |  |  |
Core deposit intangible assets | 13.6 |  |  |  |
Deferred tax assets, net | 0.2 |  |  |  |
Other assets | 7.8 |  |  |  |
Total assets acquired | 731.7 |  |  |  |
Liabilities assumed: |  |  |  |  |
Deposits | 596.6 |  |  |  |
Accounts payable and accrued expense | 18.0 |  |  |  |
Other borrowed funds | 4.1 |  |  |  |
Securities sold under repurchase agreements | 30.4 |  |  |  |
Total liabilities assumed | 649.1 |  |  |  |
Net assets acquired | 82.6 |  |  |  |
Class A common stock | 157.3 |  |  |  |
Total consideration paid | 157.3 |  |  |  |
Goodwill | $ 74.7 |  |  |  |
Northwest Bank Acquisition, As Recorded By Inland Northwest Bank |  |  |  |  |
Assets acquired: |  |  |  |  |
Cash and cash equivalents |  | $ 31.2 |  |  |
Investment securities |  | 3.1 |  |  |
Loans held for investment |  | 727.9 |  |  |
Allowance for loan loss |  | (8.0) |  |  |
Premises and equipment |  | 14.5 |  |  |
Other real estate owned (“OREO”) |  | 0.3 |  |  |
Core deposit intangible assets |  | 2.4 |  |  |
Other assets |  | 29.3 |  |  |
Total assets acquired |  | 800.7 |  |  |
Liabilities assumed: |  |  |  |  |
Deposits |  | 696.1 |  |  |
Other borrowed funds |  | 8.1 |  |  |
Long term debt |  | 13.0 |  |  |
Trust preferred securities |  | 5.2 |  |  |
Deferred tax liability, net |  | (1.2) |  |  |
Total liabilities assumed |  | 721.2 |  |  |
Net assets acquired |  | 79.5 |  |  |
Northwest Bank Acquisition, Fair Value Adjustments |  |  |  |  |
Assets acquired: |  |  |  |  |
Cash and cash equivalents |  | 0.0 |  |  |
Investment securities |  | 0.0 |  |  |
Loans held for investment |  | (14.8) |  |  |
Allowance for loan loss |  | 8.0 |  |  |
Premises and equipment |  | 0.0 |  |  |
Other real estate owned (“OREO”) |  | 0.3 |  |  |
Core deposit intangible assets |  | 13.3 |  |  |
Other assets |  | (10.0) |  |  |
Total assets acquired |  | (3.2) |  |  |
Liabilities assumed: |  |  |  |  |
Deposits |  | 0.2 |  |  |
Other borrowed funds |  | (0.4) |  |  |
Long term debt |  | 0.1 |  |  |
Trust preferred securities |  | (0.8) |  |  |
Deferred tax liability, net |  | 1.6 |  |  |
Total liabilities assumed |  | 0.7 |  |  |
Net assets acquired |  | (3.9) |  |  |
Inland Northwest Bank |  |  |  |  |
Assets acquired: |  |  |  |  |
Cash and cash equivalents |  | 31.2 |  |  |
Investment securities |  | 3.1 |  |  |
Loans held for investment |  | 713.1 |  |  |
Allowance for loan loss |  | 0.0 |  |  |
Premises and equipment |  | 14.5 |  |  |
Other real estate owned (“OREO”) |  | 0.6 |  |  |
Core deposit intangible assets |  | 15.7 |  |  |
Other assets |  | 19.3 |  |  |
Total assets acquired |  | 797.5 |  |  |
Liabilities assumed: |  |  |  |  |
Deposits |  | 696.3 |  |  |
Other borrowed funds |  | 7.7 |  |  |
Long term debt |  | 13.1 |  |  |
Trust preferred securities |  | 4.4 |  |  |
Deferred tax liability, net |  | 0.4 |  |  |
Total liabilities assumed |  | 721.9 |  |  |
Net assets acquired |  | 75.6 |  |  |
Cash |  | 3.0 |  |  |
Class A common stock |  | 173.3 |  |  |
Total consideration paid |  | 176.3 |  |  |
Goodwill |  | $ 100.7 |  |  |

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