Stockholders' Equity (Changes in Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016	Dec. 31, 2015
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Accumulated other comprehensive loss	$ (103,636)		$ (121,306)
Other comprehensive income, net of income taxes	17,670	$ 38,629
Amount, ending balance	4,032,832	3,704,402
Accumulated Other Comprehensive Income (Loss) [Member]
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Accumulated other comprehensive loss			(121,306)	$ (129,292)
Other comprehensive income (loss) before reclassifications	17,370	38,456
Amounts reclassified from accumulated other comprehensive loss (income)	300	173
Other comprehensive income, net of income taxes	17,670	38,629
Amount, ending balance	(103,636)	(90,663)
Benefits Liability, Net of Tax [Member]
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Accumulated other comprehensive loss			28,945	(8,607)
Other comprehensive income (loss) before reclassifications	101	0
Amounts reclassified from accumulated other comprehensive loss (income)	300	206
Other comprehensive income, net of income taxes	401	206
Amount, ending balance	29,346	(8,401)
Cumulative Foreign Currency Exchange, Net of Tax [Member]
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Accumulated other comprehensive loss			(150,202)	(115,690)
Other comprehensive income (loss) before reclassifications	17,344	22,805
Amounts reclassified from accumulated other comprehensive loss (income)	0	0
Other comprehensive income, net of income taxes	17,344	22,805
Amount, ending balance	(132,858)	(92,885)
Net Unrealized Holdings Gains (Losses) on Investments, Net of Tax [Member]
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Accumulated other comprehensive loss			$ (49)	$ (4,995)
Other comprehensive income (loss) before reclassifications	(75)	15,651
Amounts reclassified from accumulated other comprehensive loss (income)	0	(33)
Other comprehensive income, net of income taxes	(75)	15,618
Amount, ending balance	$ (124)	$ 10,623