Mergers and Acquisitions - Summary of the Allocation of Purchase Price to Assets and Liabilities Acquired (Details) - USD ($) $ / shares in Units, $ in Thousands			9 Months Ended
	Sep. 01, 2018	Jul. 01, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Purchase Price:
Value of stock paid			$ 434,519	$ 213,590
Increase (decrease) to net assets as a result of fair value adjustments to assets acquired and liabilities assumed:
Goodwill resulting from merger			$ 927,261	$ 611,046	$ 611,046
Brand
Purchase Price:
Shares issued to common shareholders (in shares)	9,306,477
Purchase price per share (usd per share)	$ 46.69
Value of stock paid	$ 434,519
Cash consideration paid	21,879
Cash paid for fractional shares	4
Cash settlement for stock options	17,157
Deal charges, net of taxes	894
Total Purchase Price	474,453
Increase (decrease) to net assets as a result of fair value adjustments to assets acquired and liabilities assumed:
Securities	(1,354)
Loans, net of Metropolitan’s allowance for loan losses	(16,287)
Premises and equipment	1,621
Intangible assets, net of Metropolitan’s existing intangibles	27,354
Other assets	(35)
Deposits	(1,367)
Borrowings	(3,236)
Other liabilities	13,675
Deferred income taxes	(1,029)
Total Net Assets Acquired	158,238
Goodwill resulting from merger	316,215
Brand | Brand
Net Assets Acquired:
Stockholders’ equity at acquisition date	$ 138,896
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