Stockholders' Equity (Reclassifications in Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Provision for income taxes, investments	$ (108,619)	$ 6,552	$ (232,690)	$ (129,332)
Reclassification out of Accumulated Other Comprehensive Income [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total reclassifications for the period	(336)	51,477	(1,057)	51,890
Benefits Liability, Net of Tax [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, before Tax	(529)	(369)	(1,600)	(1,072)
Other Comprehensive Income (Loss), Defined Benefit Plan, Reclassification Adjustment from AOCI, Tax	193	141	543	411
Other Comprehensive Income (Loss), Defined Benefit Plan, Reclassification Adjustment from AOCI, after Tax	(336)	(228)	(1,057)	(661)
Total reclassifications for the period			(1,057)	(661)
Net Unrealized Holdings Gains on Available-for-sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total reclassifications for the period			0	52,551
Net Unrealized Holdings Gains on Available-for-sale Securities [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Realized Gain on available for sale investments	0	52,401	0	53,720
Provision for income taxes, investments	0	(696)	0	(1,169)
Income (loss), including portion attributable to noncontrolling interest	$ 0	$ 51,705	$ 0	$ 52,551