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9. Share-based Compensation (Tables)

12 Months Ended

Dec. 31, 2018

Share-based Compensation [Abstract]

Stock Options Activity

Stock Options

The following table summarizes stock option activity:

		Shares			Weighted- Average Exercise Price				Weighted- Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value (in millions)
Outstanding, December 31, 2017		407,480			$	120.39
Granted		33,000			$	326.15
Exercised		(44,600	)		$	93.63
Forfeited/expired		(22,240	)		$	169.93
Outstanding, December 31, 2018		373,640			$	138.81			4.90		$	38.0
Unvested, December 31, 2018		99,600			$	223.91			8.32		$	3.9
Exercisable, December 31, 2018		274,040			$	107.88			3.65		$	34.1

Stock Options Valuation Assumptions

The weighted-average fair value of stock options granted was estimated using a Black-Scholes option-pricing model with the following weighted-average assumptions:

		Year Ended December 31,
		2018				2017				2016
Expected volatility		22		%		20		%		21		%
Risk-free interest rate		2.85		%		1.87		%		1.35		%
Expected life (in years)		7.6				7.2				7.4
Expected dividend		—				—				—
Weighted-average fair value of options granted		$	105.94			$	58.65			$	42.40

Resticted Stock Activity

The following table summarizes restricted stock unit activity:

		Restricted Stock Units			Weighted- Average Grant-Date Fair Value				Weighted-Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value (in millions)
Outstanding, December 31, 2017		473,000			$	172.76
Granted		185,755			$	326.15
Vested		(128,294	)		$	158.49
Forfeited		(56,011	)		$	182.15
Outstanding, December 31, 2018		474,450			$	235.57			2.11		$	110.2

Employee Stock Purchase Plan, Valuation Assumptions

The fair value of the employees’ purchase rights under the 2011 ESPP was estimated using a Black-Scholes model with the following weighted-average assumptions:

	Year Ended December 31,
	2018						2017						2016
Expected volatility	27		%				19		%				20		%
Risk-free interest rate	1.82		%				0.83		%				0.26		%
Expected life (in years)	0.24						0.24						0.25
Expected dividend	—						—						—
Weighted-average fair value
of purchase rights	$	55.04					$	38.86					$	27.36

X

- Definition

Tabular disclosure of the significant assumptions used during the year to estimate the fair value of employee stock purchase plans, including, but not limited to: (a) expected term, (b) expected volatility of the entity's shares, (c) expected dividends, (d) risk-free rate(s), and (e) discount for post-vesting restrictions.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (f)(2)
-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901

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Tabular disclosure of the significant assumptions used during the year to estimate the fair value of stock options, including, but not limited to: (a) expected term of share options and similar instruments, (b) expected volatility of the entity's shares, (c) expected dividends, (d) risk-free rate(s), and (e) discount for post-vesting restrictions.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (f)(2)
-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901

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Disclosure of the number and weighted-average grant date fair value for restricted stock and restricted stock units that were outstanding at the beginning and end of the year, and the number of restricted stock and restricted stock units that were granted, vested, or forfeited during the year.

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Tabular disclosure of the weighted-average grant-date fair value of equity options or other equity instruments granted during the year.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
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