Stockholders’ equity - Additional Information (Details) - $ / shares	3 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018
Equity [Abstract]
Cash dividends declared per common share (in dollars per share)	$ 0.77	$ 0.77	$ 0.77	$ 0.62	$ 0.62	$ 0.62
Cash dividends paid per common share (in dollars per share)	$ 0.77	$ 0.77	$ 0.77	$ 0.62	$ 0.62	$ 0.62