Earnings per share - Computation of earnings per share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017
Numerator:
Net income attributable to common shareholders	$ 311,737	$ 56,159	$ 687,448	$ 341,556
Denominator:
Basic - weighted average common shares (in shares)	130,361,273	133,112,568	131,361,464	133,144,766
Increase in weighted average common shares from dilutive effect of equity-based awards (in shares)	1,949,937	3,082,351	2,088,210	2,729,764
Diluted - weighted average common shares, assuming exercise of equity-based awards (in shares)	132,311,210	136,194,919	133,449,674	135,874,530
Basic earnings per share (in USD per share)	$ 2.39	$ 0.42	$ 5.23	$ 2.57
Diluted earnings per share (in USD per share)	$ 2.36	$ 0.41	$ 5.15	$ 2.51