Stock-based compensation (Tables)

3 Months Ended

Mar. 31, 2020

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Significant Assumptions used in Determining Fair Value of Options Granted

The following table shows the significant assumptions used in determining the fair value of options granted in the three months ended March 31, 2019 and March 31, 2020. 1,771,068 options were granted in the three months ended March 31, 2019.

	Three months ended March 31, 2019	Three months ended March 31, 2020
Dividend yield	1.08%			0.89%
Expected life (in months)	84			84
Risk-free rate of interest	2.63%		1.50%
Volatility	21.38%		20.96%

Summary of Stock Option Activity

A summary of stock option activity during the three months ended March 31, 2020 is set out below:

	Three months ended March 31, 2020
	Shares arising out of options			Weighted average exercise price		Weighted average remaining contractual life (years)				Aggregate intrinsic value
Outstanding as of January 1, 2020		8,360,212		$	25.33		6.5			$		—
Granted		431,924			43.94		—					—
Forfeited		(572,261)			27.98		—					—
Expired		—			—		—					—
Exercised		(87,528	)		14.27		—					1,307
Outstanding as of March 31, 2020		8,132,347		$	26.25		6.4			$		34,731
Vested as of March 31, 2020 and expected to vest thereafter (Note a)	7,801,794			$	25.99			6.4	$		34,397
Vested and exercisable as of March 31, 2020		3,318,511		$	19.72		3.5			$		31,454
Weighted average grant date fair value of grants during the period	$	9.72

(a)	Options expected to vest reflect an estimated forfeiture rate.

Summary of Restricted Share Units Activity

A summary of RSU activity during the three months ended March 31, 2020 is set out below:

	Three months ended March 31, 2020
	Number of Restricted Share Units			Weighted Average Grant Date Fair Value
Outstanding as of January 1, 2020		1,261,706		$	31.41
Granted		6,598			30.31
Vested (Note a)		(15,200	)		25.31
Forfeited		(518)			25.53
Outstanding as of March 31, 2020		1,252,586		$	31.48
Expected to vest (Note b)		1,155,824

(a)	15,200 RSUs that vested during the period were net settled upon vesting by issuing 10,002 shares (net of minimum statutory tax withholding).

(b)	The number of RSUs expected to vest reflects the application of an estimated forfeiture rate.

Summary of Performance Units Activity

A summary of PU activity during the three months ended March 31, 2020 is set out below:

	Three months ended March 31, 2020
	Number of Performance Units		Weighted Average Grant Date Fair Value		Maximum Shares Eligible to Receive
Outstanding as of January 1, 2020		6,058,464	$	31.07		6,058,464
Granted		339,677		43.94		679,354
Vested (Note a)		(1,496,377)		25.21		(1,496,377)
Forfeited		(230,479)		32.61		(230,479)
Adjustment upon final determination of level of performance goal achievement (Note b)		6,503		34.72		6,503
Outstanding as of March 31, 2020		4,677,788	$	33.81		5,017,465
Expected to vest (Note c)		4,004,697

(a)	1,496,377 PSUs that vested during the period were net settled upon vesting by issuing 902,532 shares (net of minimum statutory tax withholding).

(b)	Represents an adjustment made in March 2020 to the number of shares subject to the PUs granted in 2019 upon certification of the level of achievement of the performance targets underlying such awards.

(c)	The number of PUs expected to vest reflects the application of an estimated forfeiture rate.