Convertible Senior Notes - Schedule of Interest Expense (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Debt Disclosure [Abstract]
Amortization of debt discount	$ 455	$ 188
Amortization of debt issuance costs	4,796us-gaap_AmortizationOfFinancingCosts	1,990us-gaap_AmortizationOfFinancingCosts
Capitalization of interest expense	(675)us-gaap_InterestCostsCapitalized	(237)us-gaap_InterestCostsCapitalized
Interest expense	$ 4,576us-gaap_InterestExpense	$ 1,941us-gaap_InterestExpense

Amount of noncash expense included in interest expense to amortize debt discount and premium associated with the related debt instruments. Excludes amortization of financing costs. Alternate captions include noncash interest expense.

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Amount of noncash expense included in interest expense to issue debt and obtain financing associated with the related debt instruments. Alternate captions include noncash interest expense.

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Amount of interest capitalized during the period.

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-Glossary Allowance for Funds Used during Construction

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Amount of the cost of borrowed funds accounted for as interest expense.

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