Fair Value Measurements - Financial Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2016
Financial assets:
Notes receivable, net	$ 36,682	$ 32,598	$ 36,180
Investment in unconsolidated affiliate	45,605	43,319	39,875
Level 1
Financial assets:
Notes receivable, net	0	0	0
Investment in unconsolidated affiliate	42,777	49,057	38,360
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			221,950
Term Loan Facility			0
Level 3
Financial assets:
Notes receivable, net	68,720	74,262	76,012
Investment in unconsolidated affiliate	0	0	0
Financial liabilities:
Convertible Notes			0
Term Loan Facility			49,160
Carrying Value
Financial assets:
Notes receivable, net	60,025	60,975	75,545
Investment in unconsolidated affiliate	45,605	43,319	39,875
Financial liabilities:
Convertible Notes			200,728
Term Loan Facility			48,408
Estimated Fair Value
Financial assets:
Notes receivable, net	68,720	74,262	76,012
Investment in unconsolidated affiliate	42,777	49,057	38,360
Financial liabilities:
Convertible Notes			221,950
Term Loan Facility			$ 49,160
2019 Convertible Notes | Level 1
Financial liabilities:
Convertible Notes	0	0
2019 Convertible Notes | Level 2
Financial liabilities:
Convertible Notes	201,084	193,811
2019 Convertible Notes | Level 3
Financial liabilities:
Convertible Notes	0	0
2019 Convertible Notes | Carrying Value
Financial liabilities:
Convertible Notes	179,835	177,346
2019 Convertible Notes | Estimated Fair Value
Financial liabilities:
Convertible Notes	201,084	193,811
2024 Convertible Notes | Level 1
Financial liabilities:
Convertible Notes	0	0
2024 Convertible Notes | Level 2
Financial liabilities:
Convertible Notes	201,250	175,016
2024 Convertible Notes | Level 3
Financial liabilities:
Convertible Notes	0	0
2024 Convertible Notes | Carrying Value
Financial liabilities:
Convertible Notes	102,063	100,870
2024 Convertible Notes | Estimated Fair Value
Financial liabilities:
Convertible Notes	$ 201,250	$ 175,016