Shareholders' equity - Reconciliation of basic to diluted weighted average common shares outstanding (Detail) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Equity [Abstract]
Basic (in shares)	46,488	46,200	45,689
Dilutive effect of share based awards (in shares)	799	890	970
Dilutive effect of convertible notes and warrants (in shares)	0	0	142
Diluted (in shares)	47,287	47,090	46,801