Stockholders' equity - Common stock - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended
	May 06, 2021	Mar. 31, 2021	Mar. 31, 2020
Stockholders Equity Note
Cash dividends		$ 33,754	$ 35,505
Dividends Declared per Common Share		$ 0.40	$ 0.40
Dividend payable, to be paid date		Apr. 01, 2021
Dividends payable, record date		Mar. 18, 2021
Subsequent event
Stockholders Equity Note
Dividends Declared per Common Share	$ 0.45
Dividend payable, to be paid date	Jul. 01, 2020
Dividends payable, record date	May 26, 2021