Earnings per share - Reconciliation of Numerator and Denominator of Basic and Diluted Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016
Numerator:
Net income attributable to common shareholders	$ 56,159	$ 241,305	$ 341,556	$ 451,434
Denominator:
Basic - weighted average common shares	133,112,568	133,320,109	133,144,766	133,499,744
Increase in weighted average common shares from dilutive effect of equity-based awards	3,082,351	2,492,651	2,729,764	2,096,963
Diluted - weighted average common shares, assuming exercise of equity-based awards	136,194,919	135,812,760	135,874,530	135,596,707
Basic earnings per share (in USD per share)	$ 0.42	$ 1.81	$ 2.57	$ 3.38
Diluted earnings per share (in USD per share)	$ 0.41	$ 1.78	$ 2.51	$ 3.33