Changes in Accumulated Other Comprehensive Income Balances (Schedule of Changes in Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Thousands		3 Months Ended
	Jan. 01, 2018	Mar. 31, 2018	Mar. 31, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	$ 12,234	$ 12,234
Other comprehensive income:
Change in net actuarial gain		27	$ 35
Tax effect on change in net actuarial gain		(6)	(12)
Net unrealized holding gains (losses) arising during the period		(395)	5,246
Tax effect on unrealized gains arising during the period		83	(1,836)
Reclassification adjustment for gains included in net realized gains (losses)		15	(2,501)
Tax effect on reclassification adjustment for gains (losses) included in net income		(3)	875
Other comprehensive income (loss), net of tax		(279)	1,807
Reclassification of certain tax effects from accumulated other comprehensive income	(2,600)
Ending Balance		(2,419)
Minimum Pension Liability [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(2,310)	(2,310)	(2,666)
Other comprehensive income:
Change in net actuarial gain		27	35
Tax effect on change in net actuarial gain		(6)	(12)
Other comprehensive income (loss), net of tax		21	23
Reclassification of certain tax effects from accumulated other comprehensive income		(569)
Ending Balance		(2,858)	(2,643)
Unrealized Gain (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	14,544	14,544	13,037
Other comprehensive income:
Net unrealized holding gains (losses) arising during the period		(395)	5,246
Tax effect on unrealized gains arising during the period		83	(1,836)
Reclassification adjustment for gains included in net realized gains (losses)		15	(2,501)
Tax effect on reclassification adjustment for gains (losses) included in net income		(3)	875
Other comprehensive income (loss), net of tax		(300)	1,784
Reclassification of certain tax effects from accumulated other comprehensive income		3,188
Cumulative Effect of New Accounting Principle in Period of Adoption		(16,993)
Ending Balance		439	14,821
Accumulated Other Comprehensive Income [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	$ 12,234	12,234	10,371
Other comprehensive income:
Change in net actuarial gain		27	35
Tax effect on change in net actuarial gain		(6)	(12)
Net unrealized holding gains (losses) arising during the period		(395)	5,246
Tax effect on unrealized gains arising during the period		83	(1,836)
Reclassification adjustment for gains included in net realized gains (losses)		15	(2,501)
Tax effect on reclassification adjustment for gains (losses) included in net income		(3)	875
Other comprehensive income (loss), net of tax		(279)	1,807
Reclassification of certain tax effects from accumulated other comprehensive income		2,619
Cumulative Effect of New Accounting Principle in Period of Adoption		(16,993)
Ending Balance		$ (2,419)	$ 12,178