Business Combinations - Summary of Fair Value Adjustments and Goodwill (Details) - USD ($) $ in Thousands			12 Months Ended
	Jul. 02, 2018	Jan. 16, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Fair value adjustments:
Goodwill recognized from the mergers			$ 0	$ 121,910	$ 0
Premier Merger
Business Acquisition [Line Items]
Consideration transferred	$ 99,275
Cost basis of net assets on merger date	40,629
Fair value adjustments:
Investment securities	(135)
Total loans receivable, net	(111)
Other real estate owned	(1,017)
Premises and equipment	1,312
Other intangible assets	7,075
Prepaid expenses and other assets	(1,912)
Deposits	(310)
Accrued expenses and other liabilities	354
Fair value of net assets on merger date	45,885
Goodwill recognized from the mergers	$ 53,390
Puget Sound Merger
Business Acquisition [Line Items]
Consideration transferred		$ 130,773
Cost basis of net assets on merger date		54,405
Fair value adjustments:
Investment securities		(348)
Total loans receivable, net		1,400
Other real estate owned		0
Premises and equipment		(121)
Other intangible assets		9,207
Prepaid expenses and other assets		(2,282)
Deposits		(62)
Accrued expenses and other liabilities		54
Fair value of net assets on merger date		62,253
Goodwill recognized from the mergers		$ 68,520