15.	Share Plans

The Company adopted an equity incentive plan

(Plan) on

February 10, 2010

in connection with its initial public offering. The Plan, as amended, allows for granting of up to

9.1

million share-based awards to executives, directors and employees. Awards available for grant under the Plan include stock options, stock appreciation rights, restricted stock, other share-based awards and performance-based compensation awards. Total share-based compensation expense related to the Plan, net of estimated forfeitures, was

$10,205,

$9,493

and

$8,241

for the years ended

December 31, 2017,

2016

and

2015,

respectively, which is recorded in operating expenses in the consolidated statements of comprehensive income.

Stock Options

- Stock options granted in

2017

have an exercise price between

$40.12

per share and

$48.98

per share; stock options granted in

2016

have an exercise price between

$33.23

per share and

$35.37

per share, and the stock options granted in

2015

have an exercise price between

$28.36

per share and

$49.70

per share. Stock options vest in equal installments over

four

years, subject to the grantee’s continued employment or service and expire

ten

years after the date of grant.

tock option exercises can be net-share settled such that the Company withholds shares with value equivalent to the exercise price of the stock option awards plus the employees’ minimum statutory obligation for the applicable income and other employment taxes. Total shares withheld were

9,033,

473,743

and

272,296

2017,

2016

and

2015,

respectively, and were based on the value of the stock on the exercise dates. The net-share settlement has the effect of share repurchases by the Company as they reduce the number of shares that would have otherwise been issued.

Employees can also utilize a cashless for cash exercise of stock options, such that all exercised shares will be sold in the market immediately. Cash equivalent to the exercise price of the awards plus the employees

’ minimum statutory tax obligations is remitted to the Company, with the remaining cash being transferred to the employee. Total proceeds from the cashless for cash exercise of stock options were

$6,951

and

$1,623

2017

and

2016,

respectively, and are reflected as a financing activity in the consolidated statement of cash flows.

Total payments made by the Company for the employees

’ tax obligations to the taxing authorities were

$4,301,

$13,056

and

$9,768

2017,

2016

and

2015,

respectively, and are reflected as a financing activity within the consolidated statements of cash flows.

The grant-date fair value of each option grant is estimated using the Black-Scholes-Merton option pricing model. The fair value is then amortized on a straight-line basis over the requisite service period of the awards, which is generally the vesting period. Use of a valuation model requires management to make certain assumptions with respect to selected model inputs.

Expected volatility is calculated based on an analysis of historic and implied volatility measures for a set of peer companies. The average expected life is based on the contractual term of the option using the simplified method. The risk-free interest rate is based on U.S. Treasury

zero

-coupon issues with a remaining term equal to the expected life assumed at the date of grant. The compensation expense recognized is net of estimated forfeitures. Forfeitures are estimated based on actual share option forfeiture history. The weighted-average assumptions used in the Black-Scholes-Merton option pricing model for

2017,

2016

and

2015

are as follows:

	201 7			201 6			201 5
Weighted average grant date fair value	$	16.84		$	13.77		$	19.07

Assumptions:
Expected stock price volatility		40	%		41	%		41	%
Risk free interest rate		1.92	%		1.31	%		1.72	%
Expected annual dividend per share	$	-		$	-		$	-
Expected life of options (years)		6.25			6.25			6.25

The Company periodically evaluates its forfeiture rates and updates the rates it uses in the determination of its share-based compensation expense.

The impact of the change to the forfeiture rates on shares-based compensation expense was

not

material for the years ended

December 31, 2017,

2016

and

2015.

A summary of the Company

’s stock option activity and related information for the years ended

December 31, 2017,

2016

and

2015

is as follows:

	Number of Option s			Weighted- Average Exercise Pric e		Weighted- Average Remaining Contractual Term (in years )		Aggregate Intrinsic Value ($ in thousands )

Outstanding as of December 31, 201 4		2,542,139		$	9.94		8.5	$	96,518
Grante d		287,165			45.18
Exercise d		(604,088	)		3.79
Expire d		(6,409	)		50.11
Forfeite d		(90,793	)		37.27
Outstanding as of December 31, 201 5		2,128,014			15.15		7.7	$	40,271

Grante d		398,313			33.24
Exercise d		(995,469	)		2.89
Forfeite d		(47,894	)		37.41
Outstanding as of December 31, 201 6		1,482,964			27.49		7.5	$	23,840

Grante d		346,421			40.13
Exercise d		(287,375	)		10.58
Forfeite d		(69,880	)		41.12
Outstanding as of December 31, 201 7		1,472,130			33.11		7.3	$	25,281

Exercisable as of December 31, 201 7		720,730			26.76		6.1	$	17,239

As of

December 31,

201

there was

$8,552

of total unrecognized compensation cost, net of expected forfeitures, related to unvested options. The cost is expected to be recognized over the remaining service period, having a weighted-average period of

2.5

years. Total share-based compensation cost related to the stock options for

2017,

2016

and

2015

was

$4,503,

$4,366

and

$4,198,

respectively, which is recorded in operating expenses in the consolidated statements of comprehensive income.

Restricted Stock

– Restricted stock awards vest in equal installments over

three

years, subject to the grantee’s continued employment or service. Certain restricted stock awards also include performance shares, which were awarded in the years

2014

through

2017.

The number of performance shares that can be earned are contingent upon Company performance measures over a

three

-year period. Performance measures are based on a weighting of revenue growth and EBITDA margin, from which grantees

may

earn from

200%

of their target performance share award. The performance period for the

2015

awards covers the years

2015

through

2017,

the performance period for the

2016

awards covers the years

2016

through

2018,

and the performance period for the

2017

awards covers the years

2017

through

2019.

The Company estimates the number of performance shares that will vest based on projected financial performance. The fair market value of the restricted awards at the time of the grant is amortized to expense over the period of vesting. The fair value of restricted awards is determined based on the market value of the Company's shares on the grant date. The compensation expense recognized for restricted share awards is net of estimated forfeitures.

Restricted stock vesting is net-share settled such that

, upon vesting, the Company withholds shares with value equivalent to the employees’ minimum statutory obligation for the applicable income and other employment taxes, and then pays the cash to the taxing authorities on behalf of the employees. In effect, the Company repurchases these shares and classifies as treasury stock. Total shares withheld were

39,500,

28,593

and

65,763

2017,

2016

and

2015,

respectively, and were based on the value of the stock on the vesting dates. Total payments made by the Company for the employees’ tax obligations to the taxing authorities were

$1,591,

$952

and

$3,233

2017,

2016

and

2015,

respectively, and are reflected as a financing activity within the consolidated statements of cash flows.

A summary of the Company's restricted

stock activity for the years ended

December 31, 2017,

2016

and

2015

is as follows:

	Share s			Weighted- Average Grant- Date Fair Valu e

Non-vested as of December 31, 201 4		267,284		$	38.72
Grante d		193,117			41.31
Veste d		(183,362	)		32.56
Forfeite d		(33,999	)		47.77
Non-vested as of December 31, 201 5		243,040			44.16

Grante d		232,295			33.56
Veste d		(95,858	)		41.93
Forfeite d		(18,074	)		38.30
Non-vested as of December 31, 201 6		361,403			38.18

Grante d		211,769			39.91
Veste d		(133,796	)		40.60
Forfeite d		(47,100	)		42.48
Non-vested as of December 31, 201 7		392,276			37.77

As of

December 31, 2017,

there was

$7,702

of unrecognized compensation cost, net of expected forfeitures, related to non-vested restricted stock awards. That cost is expected to be recognized over the remaining service period, having a weighted-average period of

1.7

years.

Total share-based compensation cost related to the restricted stock for

2017,

2016

and

2015

was

$5,702,

$5,127

and

$4,043,

respectively, which is recorded in operating expenses in the consolidated statements of comprehensive income.

During

201

2016

and

2015,

34,095,

19,326

and

16,260

shares, respectively, of stock were granted to certain members of the Company’s Board of Directors as a component of their compensation for their service on the Board, of which

22,762,

19,326

and

16,260

shares, respectively, were fully vested. Total share-based compensation cost for these share grants in

2017,

2016

and

2015

was

$1,133,

$670

and

$615,

respectively, which is recorded in operating expenses in the consolidated statements of comprehensive income.