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Comprehensive Income (Components of Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance, December 31, 2017			$ 20,170
Amounts reclassified from AOCI, Non-credit OTTI			0
Amounts reclassified from AOCI, HTM related	$ (6)	$ (28)	(16)	$ (60)
Amounts reclassified from AOCI, All Other	2,267	(1,225)	5,861	(244)
OCI before reclassifications, Defined Benefit Pension and Post Retirement Plans			0
Amount reclassified into net income: Net actuarial loss	420	330	840	660
Other comprehensive income	(16,274)	22,407	(79,668)	40,447
Other Comprehensive Income, Defined Benefit Pension and Post Retirement Plans, Adjustment, Net of Tax	420	$ 330	840	660
Ending Balance, June 30, 2018	(84,517)		(84,517)
Available-for-sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance, December 31, 2017			80,648
Cumulative effect adjustment	(12,792)		(12,792)
OCI before reclassifications			(86,353)
Other comprehensive income			(80,492)
Ending Balance, June 30, 2018	(12,636)		(12,636)
Investments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance, December 31, 2017			80,575
Cumulative effect adjustment	(12,806)		(12,806)
OCI before reclassifications			(86,353)
Amounts reclassified from AOCI			5,845
Other comprehensive income			(80,508)
Ending Balance, June 30, 2018	(12,739)		(12,739)
Accumulated Other-than-Temporary Impairment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance, December 31, 2017			(59)
Cumulative effect adjustment	(12)		(12)
OCI before reclassifications			0
Other comprehensive income			0
Ending Balance, June 30, 2018	(71)		(71)
Accumulated Net Unrealized Investment Gain (Loss) [Member] | Held-to-maturity Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance, December 31, 2017			(14)
Cumulative effect adjustment	(2)		(2)
OCI before reclassifications			0
Other comprehensive income			(16)
Ending Balance, June 30, 2018	(32)		(32)
Accumulated Defined Benefit Plans Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance, December 31, 2017			(60,405)
Cumulative effect adjustment	(12,213)		(12,213)
Amount reclassified into net income: Net actuarial loss			840
Ending Balance, June 30, 2018	(71,778)		(71,778)
Accumulated other comprehensive income (loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance, December 31, 2017			20,170
Cumulative effect adjustment	(25,019)		(25,019)
OCI before reclassifications			(86,353)
Amounts reclassified from AOCI			6,685
Other comprehensive income			(79,668)	$ 40,447
Ending Balance, June 30, 2018	$ (84,517)		(84,517)
Adjustments for New Accounting Pronouncement [Member] | Available-for-sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance, December 31, 2017			67,856
Adjustments for New Accounting Pronouncement [Member] | Investments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance, December 31, 2017			67,769
Adjustments for New Accounting Pronouncement [Member] | Accumulated Other-than-Temporary Impairment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance, December 31, 2017			(71)
Adjustments for New Accounting Pronouncement [Member] | Accumulated Net Unrealized Investment Gain (Loss) [Member] | Held-to-maturity Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance, December 31, 2017			(16)
Adjustments for New Accounting Pronouncement [Member] | Accumulated Defined Benefit Plans Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance, December 31, 2017			(72,618)
Adjustments for New Accounting Pronouncement [Member] | Accumulated other comprehensive income (loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance, December 31, 2017			$ (4,849)

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