Securities - Additional Information (Details)	3 Months Ended
	Mar. 31, 2019 USD ($) Security	Mar. 31, 2018 USD ($)	Dec. 31, 2018 USD ($)
Schedule Of Available For Sale Securities [Line Items]
Fair value of securities sold	$ 13,900,000	$ 0
Proceeds from calls and principal repayments	2,400,000	3,800,000
Fair value of securities purchased	13,100,000	2,000,000
Impairment losses on securities	$ 0	$ 0
Number of securities in a loss position | Security	40
Other than temporary impairment recognized	$ 0
Corporate bonds with cost basis net of other-than-temporary impairment	69,679,000		$ 72,958,000
Carrying value of pledged securities	$ 16,500,000		16,500,000
Corporate Bonds [Member]
Schedule Of Available For Sale Securities [Line Items]
Number of securities in a loss position | Security	1
Corporate bonds with cost basis net of other-than-temporary impairment	$ 680,000		$ 680,000
Gain realized on sale of securities	$ 250,000