Borrowings - Balances of Liability and Equity Components (Details) (USD $)	Mar. 31, 2015	Dec. 31, 2014	Aug. 13, 2013
Debt Instrument [Line Items]
Less: debt discount	$ (25,614,000)	$ (26,662,000)
Convertible Senior Notes [Member]
Debt Instrument [Line Items]
Liability component - principal amount	287,500,000	287,500,000	287,500,000.000
Less: debt discount	(25,614,000)	(26,662,000)
Total	261,886,000	260,838,000
Equity component	$ 31,306,000	$ 31,306,000	$ 32,200,000