Share-Based Compensation

The following table presents share-based compensation expense:



	For the Three Months Ended September 30,				For the Nine Months Ended September 30,
	2017		2018		2017		2018
Share-based compensation	$	10.3	$	11.7	$	30.0	$	33.5
Tax benefit	4.0		2.9		11.5		8.4

As of December 31, 2017, the Company had unrecognized share-based compensation expense of $63.5 million. As of September 30, 2018, the Company had unrecognized share-based compensation expense of $67.1 million, which will be recognized over a weighted average period of approximately two years (assuming no forfeitures).

Stock Options

The following table summarizes transactions in the Company’s stock options:



	Stock Options		Weighted Average Exercise Price		Weighted Average Remaining Contractual Life (Years)
Unexercised options outstanding - December 31, 2017	0.6		$	122.04
Options granted	0.0		179.54
Options exercised	(0.1	)	100.00
Options forfeited	(0.0)		122.40
Unexercised options outstanding - September 30, 2018	0.5		130.30		4.0
Exercisable at September 30, 2018	0.1		136.33		2.7

For the nine months ended September 30, 2017 and 2018, the Company granted stock options with fair values of $0.8 million and $1.0 million, respectively. Stock options generally vest over a period of three to four years and expire seven years after the grant date. All options have been granted with exercise prices equal to the closing price of the Company’s common stock on the grant date. In certain circumstances, option awards also require certain performance conditions to be satisfied in order for the options to be exercised.

The fair value of options granted was estimated using the Black-Scholes option pricing model and were $48.05 and $48.64, per option, for the nine months ended September 30, 2017 and 2018, respectively. The weighted average grant date assumptions used to estimate the fair value of options granted were as follows:



	For the Nine Months Ended September 30,
	2017		2018
Dividend yield	0.5	%	0.8	%
Expected volatility	28.0	%	25.5	%
Risk-free interest rate	2.1	%	2.8	%
Expected life of options (in years)	5.7		5.7
Forfeiture rate	—	%	—	%

Restricted Stock

The following table summarizes transactions in the Company’s restricted stock units:



	Restricted Stock Units	Weighted Average Grant Date Value
Unvested units - December 31, 2017	0.4	$	162.32
Units granted	0.2	201.76
Units vested	(0.0)	198.24
Units forfeited	(0.0)	152.09
Unvested units - September 30, 2018	0.6	172.58

For the nine months ended September 30, 2017 and 2018, the Company granted restricted stock unit awards with fair values of $36.7 million and $37.7 million, respectively. These awards were valued based on the closing price of the Company’s common stock on the grant date and the number of awards expected to be delivered. Awards containing vesting conditions generally require service over a period of three to four years and may also require the satisfaction of certain performance conditions.