Stock-based Compensation Expense (Tables)

12 Months Ended

Dec. 31, 2014

The following table summarizes information about the Company’s fixed-price stock options as of and for the year ended December 31, 2014:



	Shares		Weighted-Average Exercise Price		Weighted-Average Remaining Contractual Term (Years)	Aggregate Intrinsic Value (in thousands)
Outstanding at December 31, 2013	1,369,116		$	47.55	7.0	$	22,795
Granted	222,939		63.84
Exercised	(77,546	)	34.99
Forfeited	(26,133	)	64.93
Expired	(4,133	)	62.60
Outstanding at December 31, 2014	1,484,243		$	50.30	6.5	$	17,887
Exercisable at December 31, 2014	958,599		$	42.33	5.4	$	17,887

Weighted-Average Assumptions used to Estimate Fair Value of Each Option Granted

The fair value of each option granted during the years ended December 31, 2014, 2013 and 2012 was estimated on the date of grant using the Black-Scholes option-pricing model with the following weighted-average assumptions:



	Year Ended December 31,
	2014			2013			2012
Dividend yield	1.71		%	1.58		%	1.59		%
Volatility	33.03		%	33.55		%	34.04		%
Average expected life (years)	6			6			6
Risk-free interest rate	2.94		%	2.18		%	2.05		%
Fair value of options granted	$	19.56		$	19.73		$	20.00

Activity in Performance Unit Awards

The following table summarizes activity in performance unit awards as of and for the year ended December 31, 2014:



	Shares		Weighted-Average Grant Date Fair Value Per Share
Nonvested, beginning of period	371,403		$	63.08
Granted	300,644		66.83
Vested	(116,620	)	58.02
Forfeited	(99,409	)	65.97
Nonvested, end of period	456,018		66.21

Activity in Non-Performance Based Restricted Stock Awards

The following table summarizes activity in non-performance based restricted stock and restricted stock unit awards as of and for the year ended December 31, 2014:



	Shares		Weighted-Average Grant Date Fair Value Per Share
Nonvested, beginning of period	111,195		$	59.32
Granted	44,811		60.96
Vested	(32,850	)	60.75
Forfeited	(17,868	)	48.93
Nonvested, end of period	105,288		61.34