Mergers and Acquisitions - Summary of the Allocation of Purchase Price to Assets and Liabilities Acquired (Details) - USD ($) $ / shares in Units, $ in Thousands	Jul. 01, 2017	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017
Increase (decrease) to net assets as a result of fair value adjustments to assets acquired and liabilities assumed:
Goodwill resulting from merger		$ 611,046	$ 611,046	$ 470,534
Metropolitan Bancgroup, Inc.
Purchase Price:
Shares issued to common shareholders (in shares)	4,883,182
Purchase price per share (usd per share)	$ 43.74
Value of stock paid	$ 213,590
Cash paid for fractional shares	5
Cash settlement for stock options	4,764
Deal charges, net of taxes	1,102
Total Purchase Price	219,461
Increase (decrease) to net assets as a result of fair value adjustments to assets acquired and liabilities assumed:
Securities	(731)
Mortgage loans held for sale	30
Loans, net of Metropolitan’s allowance for loan losses	(13,071)
Premises and equipment	(4,629)
Intangible assets, net of Metropolitan’s existing intangibles	2,340
Other real estate owned	(1,251)
Other assets	2,731
Deposits	(3,603)
Borrowings	(1,294)
Other liabilities	3,930
Deferred income taxes	5,244
Total Net Assets Acquired	78,949
Goodwill resulting from merger	140,512
Metropolitan Bancgroup, Inc. | Metropolitan Bancgroup, Inc.
Net Assets Acquired:
Stockholders’ equity at acquisition date	$ 89,253