Fair Value - Liabilities Measured at Fair Value on Non-Recurring Basis (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Liabilities:
Convertible senior notes	$ 312,570	$ 307,481
Total	312,570	307,481
Level 2
Liabilities:
Convertible senior notes	312,570	307,481
Fair value, measurements, nonrecurring | Level 1
Liabilities:
Convertible senior notes	0	0
Total	0	0
Fair value, measurements, nonrecurring | Level 2
Liabilities:
Convertible senior notes	312,570	307,481
Total	312,570	307,481
Fair value, measurements, nonrecurring | Level 3
Liabilities:
Convertible senior notes	0	0
Total	$ 0	$ 0