Annual report pursuant to Section 13 and 15(d)

Debt - Inputs Used In Lattice Model (Details)

v3.8.0.1
Debt - Inputs Used In Lattice Model (Details) - Notes - Notes Due February 1, 2033 - $ / shares
1 Months Ended 12 Months Ended
Apr. 01, 2015
Jan. 31, 2013
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Debt Instrument [Line Items]          
Stock price (in dollars per share)     $ 8.63 $ 9.30 $ 10.05
Conversion Rate 14.14827% 14.14827% 14.14827% 14.14827% 14.14827%
Conversion price (in dollars per share) $ 7.07 $ 7.07 $ 7.07 $ 7.07 $ 7.07
Risk-free interest rate     1.22% 1.22% 1.33%
Estimated stock volatility     49.00% 47.00% 50.00%
Estimated credit spread     7.61% 7.65% 11.42%