Debt and Interest Rate Swaps - 2020 Convertible Notes (Details) (Convertible Debt [Member], 2020 Convertible Notes [Member], USD $)
0 Months Ended 3 Months Ended
Mar. 04, 2015
Mar. 31, 2015
trading_day
Mar. 04, 2015
Debt Instrument [Line Items]      
Debt issued $ 345,000,000   $ 345,000,000
Interest rate of debt, stated percentage 0.50% 0.50% 0.50%
Initial conversion price (in usd per share) $ 28.9044   $ 28.9044
Shares issued per $1,000 principal amount 0.0345968    
Threshold trading days   20  
Consecutive trading days   30 days  
Minimum percentage of common stock price on applicable conversion price resulting in the noteholders ability to convert the notes into cash or stock   130.00%  
Threshold business days   5 days  
Measurement period   10 days  
Maximum percentage of product under last reported sale price for conversion eligibility   98.00%  
Convertible notes, percentage of principal to be paid on notes redeemed   100.00%  
Non-convertible borrowing rate (percent) 4.75%   4.75%
Interest expense   900,000  
Deferred finance costs 9,400,000   9,400,000
Other Assets [Member]      
Debt Instrument [Line Items]      
Deferred finance costs 7,700,000   7,700,000
Additional paid-in capital [Member]      
Debt Instrument [Line Items]      
Deferred finance costs $ 1,700,000   $ 1,700,000