Shareholders' equity - reconciliation of basic to diluted weighted average common shares outstanding (Detail) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Equity [Abstract]
Basic (in shares)	41,558	41,366	41,105
Dilutive effect of share based awards (in shares)	488	450	410
Dilutive effect of 3.875% Convertible Notes and warrants (in shares)	6,012	4,654	2,178
Diluted (in shares)	48,058	46,470	43,693