Fair Value Measurements - Financial Assets, Temporary Equity and Liabilities Not Measured at Fair Value (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Sep. 30, 2017	Jul. 31, 2017	Jun. 30, 2014
Financial assets:
Notes receivable, net	$ 34,199	$ 32,598
Investment in unconsolidated affiliate	49,500	43,319
Carrying Value
Financial assets:
Notes receivable, net	37,425	60,975
Investment in unconsolidated affiliate	49,500	43,319
Estimate of Fair Value Measurement
Financial assets:
Notes receivable, net	41,153	74,262
Investment in unconsolidated affiliate	49,500	49,057
Estimate of Fair Value Measurement | Level 1
Financial assets:
Notes receivable, net	0	0
Investment in unconsolidated affiliate	49,500	49,057
Estimate of Fair Value Measurement | Level 2
Financial assets:
Notes receivable, net	0	0
Investment in unconsolidated affiliate	0	0
Estimate of Fair Value Measurement | Level 3
Financial assets:
Notes receivable, net	41,153	74,262
Investment in unconsolidated affiliate	0	0
2019 Convertible Notes
Financial liabilities:
Stated interest rate				2.125%
2019 Convertible Notes | Carrying Value
Financial liabilities:
Cash Convertible Notes	187,433	177,346
2019 Convertible Notes | Estimate of Fair Value Measurement
Financial liabilities:
Cash Convertible Notes	189,150	193,811
2019 Convertible Notes | Estimate of Fair Value Measurement | Level 1
Financial liabilities:
Cash Convertible Notes	0	0
2019 Convertible Notes | Estimate of Fair Value Measurement | Level 2
Financial liabilities:
Cash Convertible Notes	189,150	193,811
2019 Convertible Notes | Estimate of Fair Value Measurement | Level 3
Financial liabilities:
Cash Convertible Notes	0	0
2024 Convertible Notes
Financial liabilities:
Stated interest rate			2.875%
2024 Convertible Notes | Carrying Value
Financial liabilities:
Cash Convertible Notes	105,858	100,870
2024 Convertible Notes | Estimate of Fair Value Measurement
Financial liabilities:
Cash Convertible Notes	180,399	175,016
2024 Convertible Notes | Estimate of Fair Value Measurement | Level 1
Financial liabilities:
Cash Convertible Notes	0	0
2024 Convertible Notes | Estimate of Fair Value Measurement | Level 2
Financial liabilities:
Cash Convertible Notes	180,399	175,016
2024 Convertible Notes | Estimate of Fair Value Measurement | Level 3
Financial liabilities:
Cash Convertible Notes	0	$ 0
2025 Convertible Notes | Carrying Value
Financial liabilities:
Cash Convertible Notes	119,736
2025 Convertible Notes | Estimate of Fair Value Measurement
Financial liabilities:
Cash Convertible Notes	161,253
2025 Convertible Notes | Estimate of Fair Value Measurement | Level 1
Financial liabilities:
Cash Convertible Notes	0
2025 Convertible Notes | Estimate of Fair Value Measurement | Level 2
Financial liabilities:
Cash Convertible Notes	161,253
2025 Convertible Notes | Estimate of Fair Value Measurement | Level 3
Financial liabilities:
Cash Convertible Notes	0
8.5% unsecured notes due 2024 | Carrying Value
Financial liabilities:
Cash Convertible Notes	$ 1,304
Stated interest rate	8.50%
8.5% unsecured notes due 2024 | Estimate of Fair Value Measurement
Financial liabilities:
Cash Convertible Notes	$ 1,304
8.5% unsecured notes due 2024 | Estimate of Fair Value Measurement | Level 1
Financial liabilities:
Cash Convertible Notes	0
8.5% unsecured notes due 2024 | Estimate of Fair Value Measurement | Level 2
Financial liabilities:
Cash Convertible Notes	0
8.5% unsecured notes due 2024 | Estimate of Fair Value Measurement | Level 3
Financial liabilities:
Cash Convertible Notes	$ 1,304