Fair Value Measurements - Financial Assets and Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Sep. 30, 2017	Mar. 31, 2017
Financial assets:
Notes receivable, net	$ 38,091	$ 32,598	$ 29,978
Investment in unconsolidated affiliate	46,509	43,319	38,334
Level 1
Financial assets:
Notes receivable, net	0	0	0
Investment in unconsolidated affiliate	46,926	49,057	37,101
Financial liabilities:
Convertible Notes			0
Term Loan Facility			0
Level 2
Financial assets:
Notes receivable, net	0	0	0
Investment in unconsolidated affiliate	0	0	0
Financial liabilities:
Convertible Notes			213,417
Term Loan Facility			0
Level 3
Financial assets:
Notes receivable, net	65,091	74,262	71,921
Investment in unconsolidated affiliate	0	0	0
Financial liabilities:
Convertible Notes			0
Term Loan Facility			50,403
Carrying Value
Financial assets:
Notes receivable, net	56,751	60,975	70,297
Investment in unconsolidated affiliate	46,509	43,319	38,334
Financial liabilities:
Convertible Notes			203,464
Term Loan Facility			48,122
Estimated Fair Value
Financial assets:
Notes receivable, net	65,091	74,262	71,921
Investment in unconsolidated affiliate	46,926	49,057	37,101
Financial liabilities:
Convertible Notes			213,417
Term Loan Facility			$ 50,403
2019 Convertible Notes | Level 1
Financial liabilities:
Convertible Notes	0	0
2019 Convertible Notes | Level 2
Financial liabilities:
Convertible Notes	206,856	193,811
2019 Convertible Notes | Level 3
Financial liabilities:
Convertible Notes	0	0
2019 Convertible Notes | Carrying Value
Financial liabilities:
Convertible Notes	182,296	177,346
2019 Convertible Notes | Estimated Fair Value
Financial liabilities:
Convertible Notes	206,856	193,811
2024 Convertible Notes | Level 1
Financial liabilities:
Convertible Notes	0	0
2024 Convertible Notes | Level 2
Financial liabilities:
Convertible Notes	212,060	175,016
2024 Convertible Notes | Level 3
Financial liabilities:
Convertible Notes	0	0
2024 Convertible Notes | Carrying Value
Financial liabilities:
Convertible Notes	103,287	100,870
2024 Convertible Notes | Estimated Fair Value
Financial liabilities:
Convertible Notes	$ 212,060	$ 175,016