Stock Based Compensation (Tables)

6 Months Ended

Jun. 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 June 30,						Six months ended June 30,
	2015			2014			2015			2014
Stock based compensation		$	15,637		$	15,442		$	29,438		$	30,013
Tax effect recognized in net income			5,473			5,405			10,303			10,505
Windfall tax benefit/(shortfall), net			4,648			4,116			8,755			11,601

Weighted average assumptions used to value option grants

	Six Months Ended June 30,
	2015		2014
Risk-free interest rate (%)		1.52		1.63
Expected option life (years)		5.10		5.24
Expected volatility (%)		22.27		27.58
Expected dividend yield (%)		0.62		0.59