Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance beginning	$ 212,366	$ 147,927	$ 150,271	$ 142,944	$ 142,944
Before reclassifications			(4,572)		427
Reclassifications			6		(152)
Balance ending	213,515	149,713	213,515	149,713	150,271
Total [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance beginning		(975)	(2,867)	(2,617)	(2,617)
Balance ending	(7,433)	$ (786)	(7,433)	(786)	(2,867)
Unrealized Gains and Losses on Available-for-Sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance beginning			(2,698)	(2,633)	(2,633)
Before reclassifications			(4,581)		585
Reclassifications			6		(152)
Balance ending	(7,273)		(7,273)		(2,698)
Changes in Pension Plan Assets and Benefit Obligations [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance beginning			(169)	$ 16	16
Before reclassifications			9		(158)
Reclassifications			0		0
Balance ending	(160)		(160)		(169)
Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance beginning			150,271
Balance ending					150,271
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Total [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance beginning	(6,383)		(2,342)
Balance ending	$ (7,433)		(7,433)		(2,342)
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Unrealized Gains and Losses on Available-for-Sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance beginning			(2,200)
Balance ending					(2,200)
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Changes in Pension Plan Assets and Benefit Obligations [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance beginning			(142)
Balance ending					$ (142)
Accounting Standards Update 2014-09 [Member] | Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Cumulative effect of changes in accounting principles			(525)
Accounting Standards Update 2014-09 [Member] | Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | Total [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Cumulative effect of changes in accounting principles			(525)
Accounting Standards Update 2014-09 [Member] | Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | Unrealized Gains and Losses on Available-for-Sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Cumulative effect of changes in accounting principles			(498)
Accounting Standards Update 2014-09 [Member] | Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | Changes in Pension Plan Assets and Benefit Obligations [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Cumulative effect of changes in accounting principles			$ (27)