Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Securities available for sale and transferred securities:Before Tax Amount
Change in net unrealized gain/loss during the period	$ 4,603	$ (3,557)
Reclassification adjustment for net gains included in net income	0	0
Reclassification adjustment for deferred tax on defined benefit postretirement medical plan	0
Total other comprehensive income	4,603	(3,557)
Securities available for sale and transferred securities: Tax (Expense) Benefit
Change in net unrealized gain/loss during the period	(968)	747
Reclassification adjustment for net gains included in net income	0	0
Reclassification adjustment for deferred tax on defined benefit postretirement medical plan	82
Total other comprehensive income	(886)	747
Securities available for sale and transferred securities: Net of Tax Amount
Change in net unrealized gain/loss during the period	3,635	(2,810)
Reclassification adjustment for net gains included in net income	0	0
Reclassification adjustment for deferred tax on defined benefit postretirement medical plan	82
Total other comprehensive income (loss)	$ 3,717	$ (2,810)