Stock Based Compensation (Tables)

9 Months Ended

Sep. 30, 2013

Notes to Financial Statements [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 endedSeptember 30,
	2013		2012		2013		2012
Stock based compensation	$	13,756	$	10,439	$	40,040	$	30,143
Tax effect recognized in net income		4,814		3,654		14,014		10,550
Windfall tax benefit, net		2,075		9,009		7,632		19,975

Weighted average assumptions used to value option grants

	Nine months ended September 30,
	2013	2012
Fair value per share ($)	36.87	30.19
Risk-free interest rate (%)	0.80	0.77
Expected option life (years)	5.19	5.24
Expected volatility (%)	36.20	36.51
Expected dividend yield (%)	0.57	0.58