STOCK-BASED PLANS (Tables)

12 Months Ended

Dec. 31, 2019

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Summary of stock option plan activity

The following table summarizes stock option activity:

					Weighted-Average
					Remaining	Aggregate
			Weighted-Average		Contractual Term	Intrinsic
	Shares		Exercise Price		(In years)	Value
Stock options outstanding at January 1, 2017	1,176,640		$	78.87
Granted	58,000		119.85
Exercised	(395,482	)	58.81
Forfeited	(54,976	)	105.17
Expired	(1,000	)	57.77
Stock options outstanding at December 31, 2017	783,182		$	90.22
Granted	265,000		$	124.56
Exercised	(183,592	)	65.72
Forfeited	(46,592	)	121.34
Stock options outstanding at December 31, 2018	817,998		$	105.06
Granted	21,500		$	105.37
Exercised	(39,402	)	63.73
Forfeited	(65,800	)	128.02
Expired	(12,800	)	143.45
Stock options outstanding at December 31, 2019	721,496		$	104.55	5.5	17,098,603
Stock options exercisable at December 31, 2019	256,296		$	76.61	2.0	13,356,723
Stock options vested and expected to vest at December 31, 2019	705,947		$	104.17	5.4	17,011,899

Summary of information related to stock options outstanding

Information related to stock options outstanding as of December 31, 2019 is summarized below:

							Weighted-Average
							Remaining
				Number	Weighted-Average		Contractual Term	Number
Range of Exercise Prices				Outstanding	Exercise Price		(In years)	Exercisable
$	46.46	$	55.82	8,775	$	48.38	1.8	8,775
$	57.77	$	60.33	131,874	58.03		1.2	131,874
$	61.64	$	69.75	47,529	66.75		2.3	47,529
$	81.80	$	110.50	75,710	103.12		5.9	33,210
$	112.64	$	151.72	457,608	123.20		7.0	34,908
				721,496	$	104.56	5.5	256,296

Summary of significant assumptions used in black-scholes option-pricing model

The fair value on the grant date and the significant assumptions used in the Black‑Scholes option‑pricing model are as follows:

	As of December 31,
	2019			2018			2017
Grant date fair value	$	32.51		$	48.27		$	34.51
Expected life of options (in years)	7.5			8.4			8.4
Risk-free interest rate	2.2		%	2.7		%	2.2		%
Expected volatility	22.6		%	24.7		%	22.8		%
Expected annual dividend per share	—			—			—

Summary of restricted stock activity

The following table summarizes restricted stock activity:

	Weighted-Average
	Grant Date
	Shares		Fair Value
Restricted stock outstanding at January 1, 2017	289,112		$	88.88
Granted	177,708		85.88
Vested	(68,819	)	88.58
Forfeited	(43,482	)	76.10
Restricted stock outstanding at December 31, 2017	354,519		$	89.00
Granted	142,332		83.09
Vested	(52,479	)	124.50
Forfeited	(37,828	)	91.71
Restricted stock outstanding at December 31, 2018	406,544		$	82.10
Granted	236,145		98.78
Vested	(118,560	)	122.51
Forfeited	(117,327	)	95.03
Restricted stock outstanding at December 31, 2019	406,802		$	76.27