Stock Based Compensation (Tables)

6 Months Ended

Jun. 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 June 30,						Six months ended June 30,
	2014			2013			2014			2013
Stock based compensation		$	15,442		$	13,307		$	30,013		$	26,284
Tax effect recognized in net income			5,405			4,658			10,505			9,199
Windfall tax benefit/(shortfall), net			4,116			1,245			11,601			5,557

Weighted average assumptions used to value option grants

	Six Months Ended June 30,
	2014		2013
Risk-free interest rate (%)		1.63		0.78
Expected option life (years)		5.24		5.19
Expected volatility (%)		27.58		36.22
Expected dividend yield (%)		0.59		0.57