Redeemable Convertible Preferred Stock (Details) (USD $) In Thousands, except Share data in Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2013 Redeemable Convertible Preferred Stock	Dec. 31, 2012 Redeemable Convertible Preferred Stock	Dec. 31, 2011 Redeemable Convertible Preferred Stock	Dec. 31, 2010 Redeemable Convertible Preferred Stock
Temporary Equity [Line Items]
Convertible Preferred Stock, Shares Issued				8.1
Preferred Stock, Dividend Rate, Percentage				6.25%
Convertible Preferred Stock, liquidation preference per share				$ 50.00
Dividends on preferred stock	$ 0	$ 2,481	$ 19,487
Conversion of redeemable convertible preferred stock	8.3
Redeemable convertible preferred stock, value				$ 0	$ 0	$ 305,032	$ 316,581