Mergers and Acquisitions - Summary of the Allocation of Purchase Price to Assets and Liabilities Acquired (Details) - USD ($) $ / shares in Units, $ in Thousands			12 Months Ended
	Sep. 01, 2018	Jul. 01, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Purchase Price:
Common stock issued in acquisition of businesses			$ 434,519	$ 213,590	$ 55,290
Increase (decrease) to net assets as a result of fair value adjustments to assets acquired and liabilities assumed:
Goodwill resulting from merger			$ 932,928	$ 611,046	$ 470,534
Brand Group Holdings, Inc.
Purchase Price:
Shares issued to common shareholders (in shares)	9,306,477
Purchase price per share (usd per share)	$ 46.69
Common stock issued in acquisition of businesses	$ 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	(231)
Loans, net of Metropolitan’s allowance for loan losses	(20,926)
Premises and equipment	910
Intangible assets, net of Metropolitan’s existing intangibles	27,534
Other assets	(3,304)
Deposits	(1,367)
Borrowings	(3,236)
Other liabilities	13,338
Deferred income taxes	957
Total net assets acquired	152,571
Goodwill resulting from merger	321,882
Brand Group Holdings, Inc. | Brand Group Holdings, Inc.
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
Common stock issued in acquisition of businesses		$ 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