Employee Share Plans (Tables)

12 Months Ended

Dec. 31, 2017

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Schedule of Fair Value Option Award Weighted Average Assumptions Used

We utilized the Black-Scholes-Merton option-pricing model to determine the fair value of stock options on the date of grant. The fair value of stock options granted during the years ended December 31, 2017, 2016 and 2015 were $3.49, $2.40, $2.34, respectively. The following weighted average assumptions were utilized:

	2017			2016			2015
Expected volatility (1)		22.22%			24.88	%		26.65	%
Expected option life (years) (2)		4.61			4.62			4.64
Risk-free interest rate (3)		1.85%			1.12	%		1.32	%
Expected dividend yield (4)		0	%		0	%		0	%

(1) The expected volatility assumption was determined based upon the historical volatility of our stock price, using daily price intervals.

(2) The expected option life was determined based upon our historical data using a midpoint scenario, which assumes all options are exercised halfway between the expiration date and the weighted average time it takes the option to vest.

(3) The risk-free interest rate assumption was upon zero-coupon U.S. Treasury bonds with a term approximating the expected life of the respective options.

(4) The expected dividend yield assumption was determined in view of our historical and estimated dividend payouts. We do not expect to change our dividend payout policy in the foreseeable future.

Schedule of Share-Based Compensation Awards

During the years ended December 31, 2017, 2016 and 2015, we recognized compensation expense for these awards as follows (in thousands):

	2017		2016		2015
Stock options	$	2,105	$	2,253	$	2,541
Restricted stock awards		3,600		3,472		3,188
Total share-based compensation expense before income    tax benefit	$	5,705	$	5,725	$	5,729

Stock Award Activity

Stock option activity during the year ended December 31, 2017 was as follows (number of options in thousands):

	Number of Options			Weighted Average Exercise Price Per Share		Weighted Average Remaining Contractual Term	Aggregate Intrinsic Value (in millions)
Outstanding at December 31, 2016		4,376		$	8.02
Granted		654		$	15.54
Exercised		(1,176	)	$	6.81
Expired or canceled		(10	)	$	7.79
Outstanding at December 31, 2017		3,844		$	9.67	3.15 years	$	22.3
Vested and exercisable at December 31,    2017		2,004		$	7.85	2.20 years	$	15.2

Roll Forward of RSU Activity

Restricted stock award activity during the year ended December 31, 2017 was as follows:

	Number of Shares (in thousands)			Weighted Average Grant-Date Fair Value (1)
Non-vested at December 31, 2016		827		$	9.14
Granted		295		$	14.90
Vested		(395	)	$	8.61
Forfeited		(3	)	$	8.36
Non-vested at December 31, 2017		724		$	11.78

(1) Represents weighted average market value of the shares as the awards are granted at no cost to the recipients.