Stock-Based Compensation (Narrative) (Detail) - USD ($)			3 Months Ended						12 Months Ended
	Oct. 16, 2014	Oct. 09, 2014	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Sep. 30, 2014	Jun. 30, 2015
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Reclassification of common unit liability to additional paid in capital									$ 490,200,000
Vesting date			May 15, 2017
Common stock distributed in connection with non-liquidating distribution		20,460,047
Total stock-based compensation expense			$ 46,100,000				$ 123,100,000
Award recorded as liability			2,400,000	$ 1,900,000					$ 1,900,000
PCIP [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Incentive plan termination period	10 years
Vested Portion of Part A Restricted Stock Units [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation expense			$ 10,000,000
Part A Restricted Stock Units [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common unit unvested			1,466,187	933,217					933,217
Total stock-based compensation expense			$ 10,000,000
Unrecognized compensation cost			17,700,000
Award recorded as liability			$ 2,400,000	$ 1,900,000					$ 1,900,000
Number of RSUs, Granted			547,635
Part B Restricted Stock Units [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares authorized			1,426,812	1,490,023	1,388,280	2,222,048			1,490,023
Common unit unvested			947,026	1,249,873					1,249,873
Total stock-based compensation expense			$ 16,400,000
Unrecognized compensation cost			$ 10,500,000
Number of RSUs, Granted			272,813	316,353	359,658	575,660
Part C Restricted Stock Units [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation expense			$ 200,000
Number of RSUs, Granted			7,952
CII [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares authorized			625,000,000
Total stock-based compensation expense			$ 100,000					$ 0
Common stock distributed in exchange for vested preferred units		256,265
CII [Member] | IPO [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common unit unvested		29,555
CII [Member] | Common Units [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common unit unvested		6,353,302
Common stock distributed for existing share holders		10,294,867
Total stock-based compensation expense			19,500,000				$ 123,100,000
Unrecognized compensation cost			$ 50,700,000