Stock Compensation Plans (Tables)

A summary of stock option activity and weighted average exercise prices follows:



	Options		Weighted- Average Exercise Price		Weighted-Average Remaining Contractual Term (Years)	Aggregate Intrinsic Value as of December 31, 2016
Outstanding at January 1, 2016	1,178,585		$	48.14
Granted	264,215		34.71
Forfeited	(217,688	)	46.57
Exercised	(111,624	)	18.10
Unearned performance-based options	(23,328	)	59.97
Outstanding at December 31, 2016	1,090,160		$	48.02	4.4	$	1,010
Options exercisable at December 31, 2016	823,512		$	40.75	2.3	$	367

The following table summarizes the restricted stock and restricted stock unit activity and weighted average grant-date fair values for the year ended December 31, 2016:



	Shares		Weighted-Average Grant Date Fair Value
Non-vested at January 1, 2016	15,916		$	43.47
Granted	159,625		33.20
Forfeited	(10,935	)	33.05
Vested	(13,247	)	42.79
Unearned performance-based awards	(677	)	53.03
Non-vested at December 31, 2016	150,682		$	33.39

For stock options granted during the years ended December 31, 2016, 2015, and 2014 valued using the Black-Scholes option valuation model, we used the following assumptions:



	Years ended December 31,
	2016		2015		2014
Risk-free interest rate	1.06% - 1.57%		0.80% - 1.21%		0.95% - 1.32%
Expected dividend yield	—	%	—	%	—	%
Expected option life	4 years		3 years		3-4 years
Expected volatility	45.0% - 47.0%		42.3% - 48.5%		42.5% - 45.4%
Weighted-average expected volatility	46.1	%	43.5	%	42.6	%

The assumptions used to estimate the fair value of the performance-based stock options and restricted stock units granted during 2015 and valued under the Monte Carlo Simulation model were as follows:



	Years Ended December 31,
	2016		2015		2014
Risk-free interest rate	—	%	0.95% - 1.48%		—	%
Expected dividend yield	—	%	—	%	—	%
Expected option life	—		4 years		—
Expected volatility	—	%	44.5	%	—	%
Weighted-average expected volatility	—	%	44.5	%	—	%