Net income (loss) per share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Basic Net Income (Loss) Per Share
Basic net income (loss) per share	$ 290,298	$ 105,318	$ (430,344)	$ 207,630
Weighted average common shares outstanding	217,549,000	214,620,000	217,135,000	214,342,000
Basic net income (loss) per share	$ 1.33	$ 0.49	$ (1.98)	$ 0.97
Diluted Net Income (Loss) Per Share
Diluted net income (loss)	$ 290,298	$ 105,318	$ (430,344)	$ 207,630
Weighted average common shares outstanding	217,549,000	214,620,000	217,135,000	214,342,000
Dilutive stock options and awards	2,885,000	2,863,000		2,932,000
Weighted average shares used to compute diluted net income (loss) per share	220,434,000	217,483,000	217,135,000	217,274,000
Diluted net income (loss) per share	$ 1.32	$ 0.48	$ (1.98)	$ 0.96
Anti-dilutive securities
Potential common shares excluded from diluted net income (loss) per share computation	5,336,636	9,534,715	14,964,275	9,590,880
Stock Options
Anti-dilutive securities
Potential common shares excluded from diluted net income (loss) per share computation	4,970,884	9,165,776	14,598,523	9,221,941
Convertible Senior Notes 1.25 Percent Due 2020
Anti-dilutive securities
Potential common shares excluded from diluted net income (loss) per share computation	365,752	368,939	365,752	368,939