Stockholders' Equity - Narrative (Details) (USD $)
In Millions, except Share data, unless otherwise specified
3 Months Ended
Mar. 31, 2015
Dec. 31, 2014
Subsidiary, Sale of Stock [Line Items]    
Common stock, shares issued (in shares) 418,935,311 411,824,039
Weighted Average    
Subsidiary, Sale of Stock [Line Items]    
Price per share (in USD per share) $ 12.07  
ATM Program    
Subsidiary, Sale of Stock [Line Items]    
Common stock, shares issued (in shares) 6,600,000  
Proceeds from issuance of common stock $ 79.8  
Net proceeds from common stock offering $ 78.6