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Comprehensive Income (Components of Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance, December 31, 2018			$ (77,956)
Amounts reclassified from AOCI, Non-credit OTTI			0
Amounts reclassified from AOCI, HTM related	$ (17)	$ (6)	(24)	$ (16)
Amounts reclassified from AOCI, All Other	(1,027)	2,267	(1,878)	5,861
OCI before reclassifications, Defined Benefit Pension and Post Retirement Plans			0
Amount reclassified into net income: Net actuarial loss	524	420	1,049	840
Other comprehensive income	65,482	(16,274)	146,462	(79,668)
Other comprehensive income, defined pension and post retirement plans	524	420	1,049	840
Ending Balance, June 30, 2019	68,506		68,506
Available-for-sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance, December 31, 2018			1,888
OCI before reclassifications			147,315
Other comprehensive income			145,437
Ending Balance, June 30, 2019	147,325		147,325
Investments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance, December 31, 2018			1,888
OCI before reclassifications			147,315
Amounts reclassified from AOCI			(1,902)
Other comprehensive income			145,413
Ending Balance, June 30, 2019	147,301		147,301
Accumulated Other-than-Temporary Impairment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance, December 31, 2018			(71)
OCI before reclassifications			0
Other comprehensive income			0
Ending Balance, June 30, 2019	(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, 2018			71
OCI before reclassifications			0
Other comprehensive income			(24)
Ending Balance, June 30, 2019	47		47
Accumulated Defined Benefit Plans Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance, December 31, 2018			(79,844)
Amount reclassified into net income: Net actuarial loss			1,049
Ending Balance, June 30, 2019	(78,795)		(78,795)
Accumulated other comprehensive income (loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance, December 31, 2018			(77,956)
OCI before reclassifications			147,315
Amounts reclassified from AOCI			(853)
Other comprehensive income	65,482	$ (16,274)	146,462	$ (79,668)
Ending Balance, June 30, 2019	$ 68,506		$ 68,506

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