Accumulated Other Comprehensive Income (Changes in AOCI by Component) (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance		$ (22,225)	$ (18,999)
Other comprehensive loss before reclassifications	[1]	(26,048)	6,306
Amounts reclassified from accumulated other comprehensive loss	[1]	(17)	87
Net current-period other comprehensive income (loss)	[1]	(26,065)	6,393
Ending balance		(48,133)	(12,606)
Unrealized Gains and Losses on Available-for-Sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance		(19,779)	(12,704)
Other comprehensive loss before reclassifications	[1]	(26,048)	1,702
Amounts reclassified from accumulated other comprehensive loss	[1]	(78)	0
Net current-period other comprehensive income (loss)	[1]	(26,126)	1,702
Ending balance		(45,748)	(11,002)
Unrealized Gains and Losses on Pension Plan Liability [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance		(2,446)	(6,295)
Other comprehensive loss before reclassifications	[1]	0	4,604
Amounts reclassified from accumulated other comprehensive loss	[1]	61	87
Net current-period other comprehensive income (loss)	[1]	61	4,691
Ending balance		$ (2,385)	$ (1,604)
Accounting Standards Update 2016-01 [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption				$ (46)
Accounting Standards Update 2016-01 [Member] | Unrealized Gains and Losses on Available-for-Sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption				157
Accounting Standards Update 2016-01 [Member] | Unrealized Gains and Losses on Pension Plan Liability [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption				0
Accounting Standards Update 2016-01 [Member] | Accumulated Other Comprehensive Income [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption				$ 157

[1] All amounts are net of tax. Amounts in parenthesis indicate debits.