Earnings per share attributable to stockholders (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Net income attributable to:
Basic	$ 60,749	$ 53,043	$ 88,937	$ 75,851
Diluted	$ 60,749	$ 53,043	$ 88,937	$ 75,851
Weighted average number of shares outstanding:
Basic	110,311,615	108,387,490	110,144,229	108,818,903
Diluted	111,334,184	109,323,343	111,302,711	109,903,808
Per Share Amount
Basic	$ 0.55	$ 0.49	$ 0.81	$ 0.70
Diluted	$ 0.55	$ 0.49	$ 0.80	$ 0.69
Share Units [Member]
Weighted average number of shares outstanding:
Effect of dilutive securities:	322,371	424,812	450,752	505,443
Stock Options [Member]
Weighted average number of shares outstanding:
Effect of dilutive securities:	700,198	511,041	707,730	579,462
Per Share Amount
Effect of dilutive securities:			(0.01)	(0.01)