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	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Purchase Price:
Common stock issued in acquisition of businesses		$ 0	$ 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		$ 939,683	$ 932,928	$ 611,046
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, net of tax benefit	17,157
Deal charges paid on behalf of Brand	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, including loans held for sale	(27,611)
Premises and equipment	910
Intangible assets	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 Group Holdings, Inc. | Brand Group Holdings, Inc.
Net Assets Acquired:
Stockholders’ equity at acquisition date	$ 138,896