Acquisitions (Narrative) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	1 Months Ended	12 Months Ended
	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2015	Dec. 31, 2013	Mar. 01, 2013
Business Acquisition [Line Items]
Dividend rate on preferred stock	3.25%	3.25%
Mandatorily redeemable convertible preferred shares redemption value		$ 125,000	$ 125,000
Jefferies [Member]
Business Acquisition [Line Items]
Conversion of stock, common shares issued	119,363
Dividend rate on preferred stock	3.25%	3.25%
Mandatorily redeemable convertible preferred shares redemption value	$ 125,000
Aggregate purchase price	$ 4,770,600
Fair value of stock on date of acquisition					$ 1,300,000
Aggregate investment in entity			$ 5,500,000
Acquisition related costs				$ 18,500
Removal of deferred tax liability reversal				$ 34,000
Jefferies [Member] | 3.875% Convertible Senior Debentures due 2029 [Member]
Business Acquisition [Line Items]
Interest rate	3.875%
Convertible Senior Debentures	$ 345,000
Conversion price per common share			$ 44.53