Fair Value Measurements - Financial Assets and Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Sep. 30, 2017	Jun. 30, 2017
Financial assets:
Notes receivable, net	$ 37,906	$ 32,598	$ 22,024
Investment in unconsolidated affiliate	61,056	43,319	41,725
Carrying Value
Financial assets:
Notes receivable, net	51,338	60,975	63,277
Investment in unconsolidated affiliate	61,056	43,319	41,725
Financial liabilities:
Term loan facility			48,235
Estimated Fair Value
Financial assets:
Notes receivable, net	57,116	74,262	65,570
Investment in unconsolidated affiliate	49,205	49,057	37,306
Financial liabilities:
Term loan facility			48,159
Estimated Fair Value | Level 1
Financial assets:
Notes receivable, net	0	0	0
Investment in unconsolidated affiliate	49,205	49,057	37,306
Financial liabilities:
Term loan facility			0
Estimated Fair Value | Level 2
Financial assets:
Notes receivable, net	0	0	0
Investment in unconsolidated affiliate	0	0	0
Financial liabilities:
Term loan facility			0
Estimated Fair Value | Level 3
Financial assets:
Notes receivable, net	57,116	74,262	65,570
Investment in unconsolidated affiliate	0	0	0
Financial liabilities:
Term loan facility			48,159
2019 Convertible Notes | Carrying Value
Financial liabilities:
Convertible notes	184,823	177,346	206,279
2019 Convertible Notes | Estimated Fair Value
Financial liabilities:
Convertible notes	197,925	193,811	218,500
2019 Convertible Notes | Estimated Fair Value | Level 1
Financial liabilities:
Convertible notes	0	0	0
2019 Convertible Notes | Estimated Fair Value | Level 2
Financial liabilities:
Convertible notes	197,925	193,811	218,500
2019 Convertible Notes | Estimated Fair Value | Level 3
Financial liabilities:
Convertible notes	0	0	$ 0
2024 Convertible Notes | Carrying Value
Financial liabilities:
Convertible notes	104,562	100,870
2024 Convertible Notes | Estimated Fair Value
Financial liabilities:
Convertible notes	195,974	175,016
2024 Convertible Notes | Estimated Fair Value | Level 1
Financial liabilities:
Convertible notes	0	0
2024 Convertible Notes | Estimated Fair Value | Level 2
Financial liabilities:
Convertible notes	195,974	175,016
2024 Convertible Notes | Estimated Fair Value | Level 3
Financial liabilities:
Convertible notes	0	$ 0
2025 Convertible Notes | Carrying Value
Financial liabilities:
Convertible notes	118,335
2025 Convertible Notes | Estimated Fair Value
Financial liabilities:
Convertible notes	168,464
2025 Convertible Notes | Estimated Fair Value | Level 1
Financial liabilities:
Convertible notes	0
2025 Convertible Notes | Estimated Fair Value | Level 2
Financial liabilities:
Convertible notes	168,464
2025 Convertible Notes | Estimated Fair Value | Level 3
Financial liabilities:
Convertible notes	$ 0