Indebtedness (Details Textual)		1 Months Ended		3 Months Ended		9 Months Ended		12 Months Ended
	Feb. 11, 2016 USD ($)	Mar. 31, 2016 USD ($) $ / shares shares	Jun. 30, 2011 USD ($) $ / shares	Sep. 30, 2016 USD ($) $ / shares	Sep. 30, 2015 USD ($)	Sep. 30, 2016 USD ($) $ / shares	Sep. 30, 2015 USD ($)	Dec. 31, 2011 USD ($) $ / shares shares	Dec. 31, 2015 USD ($)
Debt Instrument [Line Items]
Proceeds from issuance of convertible debt, net of issuance costs						$ 634,140,000
Contractual coupon interest expense				$ 900,000	$ 2,800,000	4,200,000	$ 8,300,000
Amortization of debt discount (premium)				1,300,000	4,000,000	6,300,000	11,700,000
Amortization of debt issuance costs				200,000	$ 500,000	900,000	$ 1,500,000
Derivative, maturity date								Jul. 01, 2017
Proceeds from sale of warrants						44,850,000		$ 47,900,000
Warrant strike price | $ / shares								$ 988.51
Number of common stock shares preferred stock convertible into | shares								20
Loss on repurchases of convertible notes						(17,444,000)
Revolving Senior Credit Facility [Member]
Debt Instrument [Line Items]
Credit facility, maximum borrowing capacity	$ 150,000,000
Credit facility, expiration date	2021-02
Revolving loan outstanding				0		0
Letters of Credit [Member]
Debt Instrument [Line Items]
Credit facility, maximum borrowing capacity	$ 15,000,000
Swing Line Loans [Member]
Debt Instrument [Line Items]
Credit facility, maximum borrowing capacity	$ 5,000,000
2021 Warrants [Member]
Debt Instrument [Line Items]
Proceeds from sale of warrants		$ 44,900,000
Warrant strike price | $ / shares		$ 80.00
2021 Hedge [Member]
Debt Instrument [Line Items]
Number of common stock to be purchased | shares		10,865,270
Derivative, maturity date		Mar. 15, 2021
2017 Hedge [Member]
Debt Instrument [Line Items]
Number of common stock to be purchased | shares								9,553,096
Cost of hedge transaction								$ 80,100,000
2017 Hedge [Member] | Other Expense [Member]
Debt Instrument [Line Items]
Embedded derivative, gain (loss) reclassified to earnings								$ 37,100,000
Minimum [Member]
Debt Instrument [Line Items]
Class of warrant or rights expiry month and year								2017-09
Minimum [Member] | Revolving Senior Credit Facility [Member]
Debt Instrument [Line Items]
Line of credit facility, commitment fee percentage	0.20%
Minimum [Member] | Revolving Senior Credit Facility [Member] | LIBOR [Member]
Debt Instrument [Line Items]
Credit facility bear interest rate	1.00%
Minimum [Member] | Revolving Senior Credit Facility [Member] | Base Rate [Member]
Debt Instrument [Line Items]
Credit facility bear interest rate	0.00%
Minimum [Member] | 2021 Warrants [Member]
Debt Instrument [Line Items]
Class of warrant or rights expiry month and year		2021-06
Maximum [Member]
Debt Instrument [Line Items]
Class of warrant or rights expiry month and year								2018-01
Maximum [Member] | Revolving Senior Credit Facility [Member]
Debt Instrument [Line Items]
Line of credit facility, commitment fee percentage	0.40%
Maximum [Member] | Revolving Senior Credit Facility [Member] | LIBOR [Member]
Debt Instrument [Line Items]
Credit facility bear interest rate	2.00%
Maximum [Member] | Revolving Senior Credit Facility [Member] | Base Rate [Member]
Debt Instrument [Line Items]
Credit facility bear interest rate	1.25%
Maximum [Member] | Series A Convertible Participating Preferred Stock [Member]
Debt Instrument [Line Items]
Number of preferred or common stock into which the warrants is converted | shares								477,654
Maximum [Member] | 2021 Warrants [Member]
Debt Instrument [Line Items]
Class of warrant or rights expiry month and year		2021-12
Additional Paid-in Capital [Member] | 2021 Hedge [Member]
Debt Instrument [Line Items]
Cost of hedge transaction		$ 111,200,000
Additional Paid-in Capital [Member] | 2017 Hedge [Member]
Debt Instrument [Line Items]
Amount reclassified to stockholders' equity								$ 43,000,000
Common Shares [Member] | Maximum [Member]
Debt Instrument [Line Items]
Number of preferred or common stock into which the warrants is converted | shares								9,553,080
Common Shares [Member] | Maximum [Member] | 2021 Warrants [Member]
Debt Instrument [Line Items]
Number of preferred or common stock into which the warrants is converted | shares		10,865,270
2.25% Senior Convertible Notes [Member] | Convertible Notes due 2021 [Member]
Debt Instrument [Line Items]
Principal amount		$ 650,000,000		$ 650,000,000		$ 650,000,000
Proceeds from issuance of convertible debt, net of issuance costs		$ 634,100,000
Interest rate on convertible notes		2.25%		2.25%		2.25%			2.25%
Debt instrument, maturity date		Mar. 15, 2021
Initial conversion rate adjustment, shares		16.7158
Principal amount of debt considered for conversion rate		$ 1,000
Initial conversion price of convertible notes | $ / shares		$ 59.82
Contractual coupon interest expense				$ 3,700,000		$ 7,900,000
Amortization of debt discount (premium)				3,800,000		8,200,000
Amortization of debt issuance costs				$ 600,000		$ 1,300,000
Effective interest rate				5.80%		5.80%
Debt redemption price percentage		100.00%
Principal payments due		$ 0
Fair value of debt conversion cost				$ 76,554,000		$ 76,554,000
Net proceeds of unsecured senior convertible notes		$ 345,200,000
Unamortized debt issuance costs				13,496,000		13,496,000
2.25% Senior Convertible Notes [Member] | Convertible Notes due 2021 [Member] | Scenario Two [Member]
Debt Instrument [Line Items]
Consecutive trading days considered for debt conversion		5 days
2.25% Senior Convertible Notes [Member] | Convertible Notes due 2021 [Member] | Minimum [Member]
Debt Instrument [Line Items]
Percentage of conversion price		130.00%
2.25% Senior Convertible Notes [Member] | Convertible Notes due 2021 [Member] | Minimum [Member] | Scenario One [Member]
Debt Instrument [Line Items]
Consecutive trading days considered for debt conversion		20 days
2.25% Senior Convertible Notes [Member] | Convertible Notes due 2021 [Member] | Maximum [Member]
Debt Instrument [Line Items]
Percentage of conversion price		98.00%
2.25% Senior Convertible Notes [Member] | Convertible Notes due 2021 [Member] | Maximum [Member] | Scenario One [Member]
Debt Instrument [Line Items]
Consecutive trading days considered for debt conversion		30 days
2.25% Senior Convertible Notes [Member] | Convertible Notes due 2021 [Member] | Additional Paid-in Capital [Member]
Debt Instrument [Line Items]
Amount reclassified to stockholders' equity						84,800,000
2.75% Senior Convertible Notes [Member] | Convertible Notes due 2017 [Member]
Debt Instrument [Line Items]
Principal amount		$ 125,700,000	$ 402,500,000	$ 125,732,000		$ 125,732,000			$ 402,500,000
Proceeds from issuance of convertible debt, net of issuance costs			$ 359,200,000
Interest rate on convertible notes			2.75%	2.75%		2.75%			2.75%
Debt instrument, maturity date			Jul. 01, 2017
Initial conversion rate adjustment, shares			23.7344
Principal amount of debt considered for conversion rate			$ 1,000
Initial conversion price of convertible notes | $ / shares			$ 42.13	$ 42.13		$ 42.13
Effective interest rate								8.00%
Fair value of debt conversion cost		6,800,000		$ 4,172,000		$ 4,172,000		$ 88,900,000	$ 25,958,000
Principal amount of debt instruments offering to repurchase		276,800,000
Unamortized debt issuance costs		$ 1,000,000		$ 585,000		585,000			$ 3,622,000
2.75% Senior Convertible Notes [Member] | Convertible Notes due 2017 [Member] | Other Income [Member]
Debt Instrument [Line Items]
Embedded derivative, gain (loss) reclassified to earnings								$ 39,500,000
2.75% Senior Convertible Notes [Member] | Convertible Notes due 2017 [Member] | Other Expense [Member]
Debt Instrument [Line Items]
Loss on repurchases of convertible notes						$ (17,400,000)
2.75% Senior Convertible Notes [Member] | Convertible Notes due 2017 [Member] | Scenario Two [Member]
Debt Instrument [Line Items]
Consecutive trading days considered for debt conversion								5 days
2.75% Senior Convertible Notes [Member] | Convertible Notes due 2017 [Member] | Minimum [Member]
Debt Instrument [Line Items]
Percentage of conversion price						130.00%		130.00%
2.75% Senior Convertible Notes [Member] | Convertible Notes due 2017 [Member] | Minimum [Member] | Scenario One [Member]
Debt Instrument [Line Items]
Consecutive trading days considered for debt conversion						20 days		20 days
2.75% Senior Convertible Notes [Member] | Convertible Notes due 2017 [Member] | Maximum [Member]
Debt Instrument [Line Items]
Percentage of conversion price								98.00%
2.75% Senior Convertible Notes [Member] | Convertible Notes due 2017 [Member] | Maximum [Member] | Scenario One [Member]
Debt Instrument [Line Items]
Consecutive trading days considered for debt conversion						30 days		30 days
2.75% Senior Convertible Notes [Member] | Convertible Notes due 2017 [Member] | Additional Paid-in Capital [Member]
Debt Instrument [Line Items]
Amount reclassified to stockholders' equity								$ 49,400,000