Stock Based Compensation (Tables)

9 Months Ended

Sep. 30, 2015

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,
	2015			2014			2015			2014
Stock based compensation		$	17,597		$	16,998		$	47,035		$	47,011
Tax effect recognized in net income			6,159			5,949			16,462			16,454
Windfall tax benefit/(shortfall), net			2,132			3,126			10,887			14,727

Weighted average assumptions used to value option grants

	Nine Months Ended September 30,
	2015		2014
Risk-free interest rate (%)		1.52		1.63
Expected option life (years)		5.10		5.23
Expected volatility (%)		22.23		27.27
Expected dividend yield (%)		0.62		0.59