Securities - Additional Information (Details)	12 Months Ended
	Dec. 31, 2018 USD ($) Security Bond	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Schedule Of Available For Sale Securities [Line Items]
Proceeds from calls and principal repayments	$ 11,707,000	$ 12,934,000	$ 14,222,000
Gain on sale of securities	838,000	0	1,000
Fair value of securities purchased	$ 12,400,000	34,200,000	9,900,000
Number of securities in a loss position | Security	84
Other than temporary impairment recognized	$ 0
Corporate bonds with cost basis net of other-than-temporary impairment	$ 72,958,000	72,198,000
Estimated average maturity	16 years
Anniversary on which securities could have been called at par	5 years
Frequency of repricing	3 months
Face value of corporate bond	$ 4,000,000
Gain realized on corporate bond due to auction and settlement	838,000
Interest income	26,698,000	23,320,000	21,574,000
Carrying value of pledged securities	$ 16,500,000	47,600,000
LIBOR [Member]
Schedule Of Available For Sale Securities [Line Items]
Term of variable rate	3 months
Corporate Bonds [Member]
Schedule Of Available For Sale Securities [Line Items]
Number of impaired securities | Security	1
Corporate bonds with cost basis net of other-than-temporary impairment	$ 680,000	3,816,000
Interest income	$ 112,000	$ 214,000	$ 187,000
Corporate Bonds [Member] | Performing [Member]
Schedule Of Available For Sale Securities [Line Items]
Bonds classified as performing | Bond	1