Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2014

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Schedule of Share-based Compensation, Stock Options, Activity [Table Text Block]

A summary of option activity under the Omnibus Plan as of December 31, 2014 and changes during the year then ended is presented below:

	Shares		Weighted Average Exercise Price		Weighted Average Remaining Contractual Term (in years)	Aggregate Intrinsic Value (in thousands)
Outstanding at beginning of year	969,332		$	54.32
Granted	358,469		98.31
Exercised	(326,494	)	32.67
Expired	(2,138	)	42.44
Forfeited	(15,889	)	89.82
Outstanding at end of year	983,280		$	76.99	3.1	$	15,941
Vested or expected to vest at end of year	980,480		$	76.94	3.1	$	15,940
Exercisable at end of year	442,575		$	58.91	1.9	$	13,836

Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block]

The following weighted average assumptions were used to estimate the grant date fair value of options granted during the years ended December 31, 2014, 2013 and 2012 using the Black-Scholes option pricing model:

	2014		2013		2012
Expected volatility	22	%	29	%	33	%
Expected term (in years)	4		4		4
Risk-free interest rate	1.20	%	0.89	%	0.52	%
Expected dividend yield	0	%	0	%	0	%

Schedule of Share-based Compensation, Restricted Stock and Restricted Stock Units Activity [Table Text Block]

The following table summarizes the Company's non-vested restricted stock outstanding as of December 31, 2014 and changes during the year then ended:

	Shares		Weighted Average Grant Date Fair Value
Non-vested at beginning of year	126,664		$	73.25
Granted	74,880		98.18
Vested	(73,974	)	68.80
Forfeited	(3,331	)	87.75
Non-vested at end of year	124,239		$	90.54

Schedule of Share-based Compensation, Restricted Stock Units Award Activity [Table Text Block]

The following table summarizes the Company's non-vested restricted stock units outstanding as of December 31, 2014 and changes during the year then ended:

	Shares		Weighted Average Grant Date Fair Value
Non-vested at beginning of year	93,242		$	72.78
Granted	37,007		98.24
Vested	(57,995	)	75.94
Forfeited	(6,848	)	80.73
Non-vested at end of year	65,406		$	83.55

Share-based Compensation, Performance Shares Award Unvested Activity [Table Text Block]

The following table summarizes the performance-based restricted stock units at the maximum award amounts as of December 31, 2014 and changes during the year then ended. Actual shares that will vest depending on the level of attainment of the performance-based criteria:

	Shares	Weighted Average Grant Date Fair Value
Non-vested at beginning of year	—	$	—
Granted	14,424	42.39
Vested	—	—
Forfeited	—	—
Non-vested at end of year	14,424	$	42.39

Schedule of Performance-based Units Fair Value Assumptions [Table Text Block]

The following assumptions were used to estimate the grant date fair value of the performance-based restricted stock units granted during the year ended December 31, 2014 using the Monte Carlo simulation model:

	2014
Volatility of the Company's common stock	25	%
Average volatility of peer group and S&P 500 companies	29	%
Average correlation coefficient of peer group and S&P 500 companies	0.6
Risk-free interest rate	0.81	%
Expected dividend yield	0	%
Expected term (in years)	3