Stock Based Compensation (Tables)

9 Months Ended

Sep. 30, 2014

Stock Based Compensation [Abstract]

Stock Based Compensation Expense

The following table provides information regarding the Company's stock-based compensation expense (in thousands):

	Three months ended September 30,						Nine months ended September 30,
	2014			2013			2014			2013
Stock based compensation		$	16,998		$	13,756		$	47,011		$	40,040
Tax effect recognized in net income			5,949			4,814			16,454			14,014
Windfall tax benefit/(shortfall), net			3,126			2,075			14,727			7,632

Weighted average assumptions used to value option grants

	Nine Months Ended September 30,
	2014		2013
Risk-free interest rate (%)		1.63		0.80
Expected option life (years)		5.23		5.19
Expected volatility (%)		27.27		36.20
Expected dividend yield (%)		0.59		0.57