Convertible Senior Notes - Capped Calls (Details) - USD ($) $ / shares in Units, $ in Thousands, shares in Millions	2 Months Ended	6 Months Ended
	Jul. 31, 2018	Jul. 31, 2018
Option Indexed to Issuer's Equity [Line Items]
Purchase of capped calls	$ 37,100	$ 37,086
Capped Calls
Option Indexed to Issuer's Equity [Line Items]
Strike price (in dollars per share)	$ 68.15
Cap price (in dollars per share)	$ 106.90
Capped Calls | Class A Common Stock
Option Indexed to Issuer's Equity [Line Items]
Underlying capped calls (in shares)	4.4