Stock-based Compensation - Summary of Stock Options Outstanding and Related Activity (Detail) - Employee Stock Option - HGI - $ / shares shares in Thousands	12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014
Options (in shares):
Stock options outstanding at September 30, 2015	4,770
Granted	28	977	1,356
Exercised	(567)
Stock options outstanding at September 30, 2016	4,231	4,770
Stock options vested and exercisable at September 30, 2016	3,273
Stock options outstanding and expected to vest	4,231
Weighted Average Exercise Price (in dollars per share):
Stock options outstanding at September 30, 2015	$ 9.25
Granted	13.93
Exercised	7.82
Stock options outstanding at September 30, 2016	9.48	$ 9.25
Stock options vested and exercisable at September 30, 2016	8.56
Stock options outstanding and expected to vest	9.48
Weighted Average Grant Date Fair Value (in dollars per share):
Stock options outstanding at September 30, 2015	3.70
Granted	5.07
Exercised	3.05
Stock options outstanding at September 30, 2016	3.80	$ 3.70
Stock options vested and exercisable at September 30, 2016	3.42
Stock options outstanding and expected to vest	$ 3.80