Stock-Based Compensation and Employee Benefit Plans (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	12 Months Ended
	Nov. 30, 2010	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2013
Holdings
Stock-Based Compensation and Employee Benefit Plans
Dividend paid		$ 445,537	$ 721,682
Senior management
Additional disclosures
Reduction in percentage of share-based compensation expense for estimated forfeitures		0.00%
Other management
Additional disclosures
Reduction in percentage of share-based compensation expense for estimated forfeitures		5.00%
Stock option
Stock-Based Compensation and Employee Benefit Plans
Expiration period	10 years
Vesting period		5 years
Number of shares
Outstanding at beginning of period (in shares)		139,647	173,183
Granted (in shares)		106,530	13,430
Exercised (in shares)		(9,554)	(614)
Forfeited (in shares)		(18,220)	(46,352)
Outstanding at end of period (in shares)		218,403	139,647	173,183
Exercisable at end of period (in shares)		57,923	50,360
Number of shares available for future grant (in shares)		32,676
Weighted average exercise price
Outstanding at beginning of period (in dollars per share)		$ 212	$ 179
Granted (in dollars per share)		373	473
Exercised (in dollars per share)		150	133
Forfeited (in dollars per share)		268	153
Outstanding at end of period (in dollars per share)		289	212	$ 179
Exercisable at end of period (in dollars per share)		$ 190	152
Stock option | Time-based awards
Stock-Based Compensation and Employee Benefit Plans
Vesting period		5 years
Weighted-average grant date fair value (in dollars per share)		$ 125	$ 147	$ 167
Weighted-average assumptions used for the options granted
Risk-free rate, minimum (as a percent)		0.01%	0.00%	0.11%
Risk-free rate, maximum (as a percent)		3.07%	3.65%	4.59%
Expected term		6 years 6 months	6 years 6 months	6 years 6 months
Expected volatility (as a percent)		37.00%	37.00%	36.00%
Expected dividends (as a percent)		0.00%	0.00%	0.00%
Stock option | Performance based awards
Stock-Based Compensation and Employee Benefit Plans
Compensation deduction for tax purposes		$ 0	$ 0
Weighted-average grant date fair value (in dollars per share)		$ 66	$ 98	$ 96
Weighted-average assumptions used for the options granted
Risk-free rate, minimum (as a percent)		0.01%	0.02%	0.11%
Risk-free rate, maximum (as a percent)		3.07%	3.65%	4.59%
Expected term		4 years 3 months 18 days	3 years 1 month 6 days	4 years 6 months
Expected volatility (as a percent)		33.00%	33.00%	37.00%
Expected dividends (as a percent)		0.00%	0.00%	0.00%
Class A Common stock
Stock-Based Compensation and Employee Benefit Plans
Aggregate number of shares which may be issued	19,367
Class B Common stock
Stock-Based Compensation and Employee Benefit Plans
Aggregate number of shares which may be issued	239,305
Class B Common stock | Stock option
Number of shares
Granted (in shares)		106,530	13,430	19,180