Stockholders' Equity (Changes in Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015	Dec. 31, 2014
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss (income), balance	$ 3,737,436	$ 3,417,175	$ 3,737,436	$ 3,417,175	$ 3,561,931	$ 3,201,888
Amounts reclassified from accumulated other comprehensive loss (income)	(585)	(1,992)	(412)	(1,565)
Other comprehensive income (loss)	8,562	17,738	47,191	(40,491)
Benefits Liability, Net of Tax [Member}
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss (income), balance	(8,301)	(22,690)	(8,301)	(22,690)	(8,607)	(23,442)
Other comprehensive income (loss) before reclassifications			(127)	(115)
Amounts reclassified from accumulated other comprehensive loss (income)	227	440	433	867
Other comprehensive income (loss)			306	752
Cumulative Foreign Currency Exchange [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss (income), balance	(106,385)	(98,050)	(106,385)	(98,050)	(115,690)	(56,224)
Other comprehensive income (loss) before reclassifications			9,305	(41,826)
Amounts reclassified from accumulated other comprehensive loss (income)			0	0
Other comprehensive income (loss)			9,305	(41,826)
Net Unrealized Holdings (Losses) Gains on Investments, Net of Tax [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss (income), balance	32,585	816	32,585	816	(4,995)	233
Other comprehensive income (loss) before reclassifications			38,425	3,015
Amounts reclassified from accumulated other comprehensive loss (income)			(845)	(2,432)
Other comprehensive income (loss)			37,580	583
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss (income), balance	$ (82,101)	$ (119,924)	(82,101)	(119,924)	$ (129,292)	$ (79,433)
Other comprehensive income (loss) before reclassifications			47,603	(38,926)
Amounts reclassified from accumulated other comprehensive loss (income)			(412)	(1,565)
Other comprehensive income (loss)			$ 47,191	$ (40,491)