Long-term Debt (Details) (USD $) Share data in Millions, except Per Share data, unless otherwise specified	1 Months Ended	3 Months Ended		9 Months Ended			0 Months Ended	1 Months Ended		3 Months Ended	9 Months Ended			3 Months Ended	0 Months Ended
	Apr. 30, 2013	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012	May 28, 2012 Convertible Debt [Member] Director [Member] Senior Convertible Note [Member]	Apr. 30, 2013 Convertible Debt [Member] Director [Member] Senior Convertible Note [Member]	Nov. 30, 2011 Convertible Debt [Member] Director [Member] Senior Convertible Note [Member]	Mar. 31, 2013 Senior Notes [Member] 5.375% Senior Notes [Member]	Sep. 30, 2013 Senior Notes [Member] 5.375% Senior Notes [Member]	Feb. 28, 2013 Senior Notes [Member] 5.375% Senior Notes [Member]	Sep. 30, 2013 Senior Notes [Member] 5.375% Senior Notes [Member] Level 2 Securities [Member]	Mar. 31, 2013 Senior Notes [Member] 8.50% Senior Notes [Member]	May 28, 2012 Minimum [Member] Convertible Debt [Member] Director [Member] Senior Convertible Note [Member]	May 28, 2012 Maximum [Member] Convertible Debt [Member] Director [Member] Senior Convertible Note [Member]
Debt Instrument [Line Items]
Long-term debt due to related party		$ 0		$ 0		$ 200,000,000			$ 200,000,000
Weighted average price of common stock							$ 111.54
Trading days prior to conversion date required for conversion															50 days	65 days
Common stock, shares issued	2.3							2.3
Common stock conversion ratio								11.6553
Fair value at conversion								$ 216.99
Face amount												500,000,000		200,000,000
Interest rate									0.00%		5.375%	5.375%		8.50%
Redemption prices, percent of outstanding principal											101.00%
Repayments		0	0	219,362,000	0					224,500,000
Make-whole premium														19,400,000
Interest payable														5,100,000
Loss on extinguishment of debt		0	0	(25,129,000)	0									25,100,000
Write off of unamortized deferred financing costs														4,200,000
Senior notes, fair value													$ 496,300,000