Stockholders’ Equity - Narrative (Details)	3 Months Ended	75 Months Ended
	Dec. 31, 2018 item $ / shares shares	Dec. 31, 2018 shares
RSUs
Stockholders' Equity
Number of shares of common stock that each award holder has the contingent right to receive	1
Fair value units granted (per share) | $ / shares	$ 64.33
Time-based RSUs
Stockholders' Equity
Number of units awarded (in shares)		1,285,560
Number of equal installments for vesting of stock awards | item	4
Expected awards vested (in shares)	331,181
Performance-based RSUs
Stockholders' Equity
Number of units awarded (in shares)		1,173,766
Vesting period	3 years
Number of vesting criteria which have to be satisfied out of total vesting criteria | item	1
Number of vesting criteria | item	3
Expected awards vested (in shares)	129,907
Performance and market-based RSUs
Stockholders' Equity
Number of units awarded (in shares)		219,890
Number of shares of common stock that each award holder has the contingent right to receive	1.25
Vesting period	3 years
Fair value units granted (per share) | $ / shares	$ 67.40
Expected awards vested (in shares)	152,570
Performance and market-based RSUs | Maximum
Stockholders' Equity
Increase in multiplier based on performance	25.00%
Performance and market-based RSUs | Minimum
Stockholders' Equity
Decrease in multiplier based on performance	25.00%