Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance beginning	$ 218,985	$ 150,271	$ 150,271
Before reclassifications	2,475		(1,858)
Reclassifications	14		6
Balance ending	224,018	148,584	218,985
Total [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance beginning		(2,867)	(2,867)
Balance ending	(2,230)	(5,843)
Unrealized Gains and Losses on Available-for-Sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance beginning		(2,698)	(2,698)
Before reclassifications	2,475		(1,939)
Reclassifications	14		6
Balance ending	(2,142)
Changes in Pension Plan Assets and Benefit Obligations [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance beginning		(169)	(169)
Before reclassifications	0		81
Reclassifications	0		0
Balance ending	(88)
Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance beginning	218,985
Balance ending			218,985
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Total [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance beginning	(4,719)	(2,342)	(2,342)
Balance ending	(2,230)		(4,719)
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	(4,631)	(2,200)	(2,200)
Balance ending			(4,631)
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	$ (88)	(142)	(142)
Balance ending			(88)
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)