Acquisition of First Priority Financial Corp. (Narrative) (Details) - USD ($)		12 Months Ended
	Jul. 31, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Business Acquisition [Line Items]
Goodwill		$ 62,840,000	$ 62,840,000
Amortization expense		1,398,000	1,430,000	$ 1,224,000
First Priority Financial Corp. [Member]
Business Acquisition [Line Items]
Acquisition completion date	Jul. 31, 2018
Shares of acquirer ratio of common stock	34.81%
Per share price	$ 11.07
Common stock shares issued to acquire the company	2,320,800
Business combination, consideration transferred, equity interests issued and issuable	$ 76,122,000
Payments to acquire businesses gross	3,807,000
Business combination consideration transferred	79,929,000
Goodwill	39,744,000
Intangible assets acquired (finite lived)	2,832,000
Intangible assets acquired (indefinite lived)	$ 205,000
Intangible assets, amortization period	10 years
Core deposit intangible amortization expense related to acquisition for year one	$ 390,000
Core deposit intangible amortization expense related to acquisition for year two	339,000
Core deposit intangible amortization expense related to acquisition for year three	288,000
Core deposit intangible amortization expense related to acquisition for year four	236,000
Core deposit intangible amortization expense related to acquisition for year five	185,000
Core deposit intangible amortization expense related to acquisition for four years after year five	244,000
Fair value of purchased loans	$ 511,623,000
Pro forma earnings				15,469,000	$ 9,170,000
Severance and retention bonus expenses				1,475,000
First Priority Financial Corp. [Member] | Excluded Acquisition-related Costs [Member]
Business Acquisition [Line Items]
Pro forma earnings				3,486,000
Income tax nondeductible expenses				$ 714,000
First Priority Financial Corp. [Member] | Core Deposits [Member]
Business Acquisition [Line Items]
Amortization expense		$ 442,000	$ 493,000
First Priority Financial Corp. [Member] | Series D [Member]
Business Acquisition [Line Items]
Preferred Stock, Shares Issued	3,404
Preferred stock, value	$ 3,404,000
First Priority Financial Corp. [Member] | Stock Options [Member]
Business Acquisition [Line Items]
Payments to acquire businesses gross	3,801,000
First Priority Financial Corp. [Member] | Fractional Shares [Member]
Business Acquisition [Line Items]
Payments to acquire businesses gross	$ 6,000
First Priority Financial Corp. [Member] | Common Stock [Member]
Business Acquisition [Line Items]
Per share price	$ 32.80
Business combination, consideration transferred, equity interests issued and issuable	$ 76,122,000