Income Taxes - Additional Information (Detail) - USD ($)	3 Months Ended								12 Months Ended
	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Income Taxes [Line Items]
Net tax benefit	$ (1,852,000)	$ (9,094,000)	$ (1,484,000)	$ (1,831,000)	$ (678,000)	$ (9,285,000)	$ (1,497,000)	$ (748,000)	$ (14,261,000)	$ (12,208,000)	$ 27,414,000
Reduction in income tax provision					1,100,000
Decrease in uncertain tax positions	264,000								264,000
Effective tax rate impact on prior year tax position	177,000
Unrecognized tax benefits	0				254,000				0	254,000	$ 244,000
Impact on effective tax rate if recognized	0				154,000				0	154,000
Interest and penalties									0	130,000
Domestic Country
Income Taxes [Line Items]
Net operating loss (NOL) carryforwards	0				$ 21,000,000				$ 0	$ 21,000,000
Operating loss carry forwards expiration year										2031
Share based compensation expenses excludes from net operating loss carryforwards										$ 14,600,000
Maximum [Member] | State And Local Jurisdiction
Income Taxes [Line Items]
Operating loss carry forwards expiration year									2032
British Virgin Islands [Member]
Income Taxes [Line Items]
Net tax benefit	$ 1,800,000