Stock-based compensation plans (Tables)

12 Months Ended

Dec. 31, 2016

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Summary of Restricted Stock and Restricted Stock Unit Activity

A summary of restricted stock and restricted stock unit activity follows:

	Restricted Stock Units Outstanding			Weighted- Average Grant Price		Restricted Stock Outstanding			Weighted- Average Grant Price
Unvested at January 1, 2016		968,498		$	109.38		625,888		$	103.82
Granted		348,297			111.38		218,341			110.31
Vested		(570,509	)		108.21		(324,981	)		98.55
Cancelled		(6,936	)		110.90		(19,924	)		108.15
Unvested at December 31, 2016		739,350		$	111.21		499,324		$	109.92

Summary of Stock Option Activity

A summary of stock option activity follows:

				Weighted-Average
	Stock Options Outstanding			Exercise Price		Life (In Years)		Aggregate Intrinsic Value (In thousands)
Outstanding at January 1, 2016		4,223,710		$	126.65
Granted		200			110.18
Exercised		(1,694,440	)		106.68
Expired		(934,879	)		140.75
Outstanding at December 31, 2016		1,594,591		$	139.60		1.5	$	39,326
Exercisable at December 31, 2016		1,594,149		$	139.60		1.5	$	39,305