Fair Value Measurements - Financial Assets and Liabilities not Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Sep. 30, 2018	Dec. 31, 2017	Jul. 31, 2017	Jun. 30, 2014
Financial assets:
Notes receivable, net	$ 26,711	$ 34,199	$ 36,682
Investment in unconsolidated affiliate	$ 35,511	49,500	45,605
Level 1
Financial assets:
Notes receivable, net		0	0
Investment in unconsolidated affiliate		49,500	42,777
Level 2
Financial assets:
Notes receivable, net		0	0
Investment in unconsolidated affiliate		0	0
Level 3
Financial assets:
Notes receivable, net		41,153	68,720
Investment in unconsolidated affiliate		0	0
Notes Receivable | Minimum | Disposal Group | Grupo Finmart
Financial liabilities:
Derivative measurement input	0.07
Notes Receivable | Maximum | Disposal Group | Grupo Finmart
Financial liabilities:
Derivative measurement input	0.08
Carrying Value
Financial assets:
Notes receivable, net	$ 31,310	37,425	60,025
Investment in unconsolidated affiliate	35,511	49,500	45,605
Estimated Fair Value
Financial assets:
Notes receivable, net	33,710	41,153	68,720
Investment in unconsolidated affiliate	35,511	49,500	42,777
Estimated Fair Value | Level 1
Financial assets:
Notes receivable, net	0
Investment in unconsolidated affiliate	35,511
Estimated Fair Value | Level 2
Financial assets:
Notes receivable, net	0
Investment in unconsolidated affiliate	0
Estimated Fair Value | Level 3
Financial assets:
Notes receivable, net	33,710
Investment in unconsolidated affiliate	0
2019 Convertible Notes
Financial liabilities:
Stated interest rate					2.125%
2019 Convertible Notes | Level 1
Financial liabilities:
Convertible notes		0	0
2019 Convertible Notes | Level 2
Financial liabilities:
Convertible notes		189,150	201,084
2019 Convertible Notes | Level 3
Financial liabilities:
Convertible notes		0	0
2019 Convertible Notes | Carrying Value
Financial liabilities:
Convertible notes	190,076	187,433	179,835
2019 Convertible Notes | Estimated Fair Value
Financial liabilities:
Convertible notes	190,613	189,150	201,084
2019 Convertible Notes | Estimated Fair Value | Level 1
Financial liabilities:
Convertible notes	0
2019 Convertible Notes | Estimated Fair Value | Level 2
Financial liabilities:
Convertible notes	190,613
2019 Convertible Notes | Estimated Fair Value | Level 3
Financial liabilities:
Convertible notes	0
2024 Convertible Notes
Financial liabilities:
Stated interest rate				2.875%
2024 Convertible Notes | Level 1
Financial liabilities:
Convertible notes		0	0
2024 Convertible Notes | Level 2
Financial liabilities:
Convertible notes		180,399	201,250
2024 Convertible Notes | Level 3
Financial liabilities:
Convertible notes		0	0
2024 Convertible Notes | Carrying Value
Financial liabilities:
Convertible notes	107,182	105,858	102,063
2024 Convertible Notes | Estimated Fair Value
Financial liabilities:
Convertible notes	145,202	180,399	$ 201,250
2024 Convertible Notes | Estimated Fair Value | Level 1
Financial liabilities:
Convertible notes	0
2024 Convertible Notes | Estimated Fair Value | Level 2
Financial liabilities:
Convertible notes	145,202
2024 Convertible Notes | Estimated Fair Value | Level 3
Financial liabilities:
Convertible notes	0
2025 Convertible Notes | Level 1
Financial liabilities:
Convertible notes		0
2025 Convertible Notes | Level 2
Financial liabilities:
Convertible notes		161,253
2025 Convertible Notes | Level 3
Financial liabilities:
Convertible notes		0
2025 Convertible Notes | Carrying Value
Financial liabilities:
Convertible notes	121,316	119,736
2025 Convertible Notes | Estimated Fair Value
Financial liabilities:
Convertible notes	134,447	161,253
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	134,447
2025 Convertible Notes | Estimated Fair Value | Level 3
Financial liabilities:
Convertible notes	0
8.5% unsecured notes due 2024 | Level 1
Financial liabilities:
Secured and unsecured debt		0
8.5% unsecured notes due 2024 | Level 2
Financial liabilities:
Secured and unsecured debt		0
8.5% unsecured notes due 2024 | Level 3
Financial liabilities:
Secured and unsecured debt		1,304
8.5% unsecured notes due 2024 | Carrying Value
Financial liabilities:
Secured and unsecured debt	$ 1,237	$ 1,304
Stated interest rate	8.50%	8.50%
8.5% unsecured notes due 2024 | Estimated Fair Value
Financial liabilities:
Secured and unsecured debt	$ 1,237	$ 1,304
8.5% unsecured notes due 2024 | Estimated Fair Value | Level 1
Financial liabilities:
Secured and unsecured debt	0
8.5% unsecured notes due 2024 | Estimated Fair Value | Level 2
Financial liabilities:
Secured and unsecured debt	0
8.5% unsecured notes due 2024 | Estimated Fair Value | Level 3
Financial liabilities:
Secured and unsecured debt	1,237
CASHMAX secured borrowing facility | Carrying Value
Financial liabilities:
Secured and unsecured debt	334
CASHMAX secured borrowing facility | Estimated Fair Value
Financial liabilities:
Secured and unsecured debt	1,160
CASHMAX secured borrowing facility | Estimated Fair Value | Level 1
Financial liabilities:
Secured and unsecured debt	0
CASHMAX secured borrowing facility | Estimated Fair Value | Level 2
Financial liabilities:
Secured and unsecured debt	0
CASHMAX secured borrowing facility | Estimated Fair Value | Level 3
Financial liabilities:
Secured and unsecured debt	$ 1,160