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	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Purchase Price:
Value of stock paid		$ 0	$ 434,519
Increase (decrease) to net assets as a result of fair value adjustments to assets acquired and liabilities assumed:
Goodwill resulting from merger		$ 939,683	$ 927,261	$ 932,928
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	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	(323)
Loans, net of Metropolitan’s allowance for loan losses	(27,611)
Premises and equipment	910
Intangible assets, net of Metropolitan’s existing intangibles	27,534
Other assets	(4,495)
Deposits	(1,367)
Borrowings	(2,023)
Other liabilities	13,338
Deferred income taxes	957
Total Net Assets Acquired	145,816
Goodwill resulting from merger	328,637
Brand | Brand
Net Assets Acquired:
Stockholders’ equity at acquisition date	$ 138,896