Debt - Convertible Notes Hedge Transactions, Conversion and EPS Impact (Details)	3 Months Ended	9 Months Ended
	Dec. 31, 2013 d	Sep. 30, 2017 USD ($) $ / shares	Sep. 30, 2016 USD ($)	Mar. 05, 2014 $ / shares	Jun. 24, 2013 $ / shares	Nov. 27, 2012 $ / shares
Debt Instrument [Line Items]
Proceeds from convertible hedge instruments		$ 5,580,000	$ 0
Reclassifications of equity to temporary equity, debt conversion (less than)		100,000
2017 Convertible Senior Notes
Debt Instrument [Line Items]
Cost of the hedge transaction(s)		50,595,000
Conversion price (in dollars per share) | $ / shares						$ 31.56
Convertible debt, threshold of stock price trigger (exceeded)	130.00%
Convertible debt, threshold trading days | d	20
Convertible debt, threshold consecutive trading days | d	30
Convertible notes, fair value		90,500,000
Amount of converted notes		0
2020 Convertible Notes
Debt Instrument [Line Items]
Cost of the hedge transaction(s)		18,113,000
Conversion price (in dollars per share) | $ / shares					$ 45.72
2021 Convertible Notes
Debt Instrument [Line Items]
Cost of the hedge transaction(s)		$ 19,545,000
Conversion price (in dollars per share) | $ / shares				$ 59.39
Hedging of Convertible Debt Instrument | 2017 Convertible Senior Notes
Debt Instrument [Line Items]
Conversion price (in dollars per share) | $ / shares		$ 60.00
Hedging of Convertible Debt Instrument | 2020 Convertible Notes
Debt Instrument [Line Items]
Conversion price (in dollars per share) | $ / shares		61.55
Hedging of Convertible Debt Instrument | 2021 Convertible Notes
Debt Instrument [Line Items]
Conversion price (in dollars per share) | $ / shares		$ 83.14