Securities, Securities in Continuous Unrealized Loss Position (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018 USD ($) Security	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($) Security Bond	Sep. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)
Securities in Continuous Unrealized Loss Position [Abstract]
Less than 12 months, fair value	$ 50,679		$ 50,679		$ 37,066
Less than 12 months, unrealized (losses)	(1,284)		(1,284)		(394)
12 months or more, fair value	16,990		16,990		11,548
12 months or more, unrealized (losses)	(852)		(852)		(431)
Total, fair value	67,669		67,669		48,614
Total, unrealized (losses)	$ (2,136)		$ (2,136)		(825)
Impaired Securities [Abstract]
Number of securities in a loss position | Security	95		95
Corporate bonds with cost basis net of other-than-temporary impairment	$ 74,557		$ 74,557		72,198
Estimated maturity			16 years
Anniversary on which securities could have been called at par			5 years
Frequency of repricing			3 months
Interest income	6,694	$ 6,001	$ 19,604	$ 17,129
LIBOR [Member]
Impaired Securities [Abstract]
Term of variable rate			3 months
Obligations of U.S. Government Corporations and Agencies [Member]
Securities in Continuous Unrealized Loss Position [Abstract]
Less than 12 months, fair value	40,066		$ 40,066		32,512
Less than 12 months, unrealized (losses)	(1,047)		(1,047)		(330)
12 months or more, fair value	15,829		15,829		10,008
12 months or more, unrealized (losses)	(802)		(802)		(278)
Total, fair value	55,895		55,895		42,520
Total, unrealized (losses)	(1,849)		(1,849)		(608)
Impaired Securities [Abstract]
Corporate bonds with cost basis net of other-than-temporary impairment	59,228		59,228		52,872
Obligations of States and Political Subdivisions [Member]
Securities in Continuous Unrealized Loss Position [Abstract]
Less than 12 months, fair value	10,613		10,613		4,172
Less than 12 months, unrealized (losses)	(237)		(237)		(60)
12 months or more, fair value	1,161		1,161		0
12 months or more, unrealized (losses)	(50)		(50)		0
Total, fair value	11,774		11,774		4,172
Total, unrealized (losses)	(287)		(287)		(60)
Impaired Securities [Abstract]
Corporate bonds with cost basis net of other-than-temporary impairment	$ 14,655		$ 14,655		15,124
Corporate Bonds [Member]
Securities in Continuous Unrealized Loss Position [Abstract]
Less than 12 months, fair value					0
Less than 12 months, unrealized (losses)					0
12 months or more, fair value					1,540
12 months or more, unrealized (losses)					(153)
Total, fair value					1,540
Total, unrealized (losses)					(153)
Impaired Securities [Abstract]
Number of impaired securities | Security	1		1
Corporate bonds with cost basis net of other-than-temporary impairment	$ 674		$ 674		3,816
Interest income	18	$ 55	$ 97	$ 158
Corporate Bonds [Member] | Performing [Member]
Impaired Securities [Abstract]
Bonds classified as performing | Bond			1
Mutual Funds [Member]
Securities in Continuous Unrealized Loss Position [Abstract]
Less than 12 months, fair value					382
Less than 12 months, unrealized (losses)					(4)
12 months or more, fair value					0
12 months or more, unrealized (losses)					0
Total, fair value					382
Total, unrealized (losses)					(4)
Impaired Securities [Abstract]
Corporate bonds with cost basis net of other-than-temporary impairment					$ 386
2 Corporate Bond [Member]
Impaired Securities [Abstract]
Face value of corporate bond	$ 4,000		$ 4,000
Gain realized on corporate bond due to auction and settlement			$ 838