Stockholders' equity (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended				9 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Stockholders' Equity Note [Abstract]
Dividends declared on common stock	$ 173,561	$ 170,600	$ 160,800	$ 143,040	$ 504,986	$ 406,702
Dividends declared on common stock (per share)	$ 1.12	$ 1.12	$ 1.09	$ 1.06	$ 3.33	$ 3.15
Shares of common stock authorized	200,000,000				200,000,000
Shares of common stock issued and outstanding	153,300,000				153,300,000
Shares of preferred stock authorized	100,000,000				100,000,000
Shares of preferred stock issued and outstanding	0				0
Number of "excess stock" authorized (in shares)					200,000,000
Number of excess stock authorized issued and outstanding (in shares)	0				0