Stock Based Compensation (Tables)

6 Months Ended

Jun. 30, 2016

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,
	2016			2015			2016			2015
Stock based compensation		$	20,113		$	15,637		$	39,092		$	29,438
Tax effect recognized in net income			7,040			5,473			13,682			10,303
Windfall tax benefit/(shortfall), net			-			4,648			-			8,755

Windfall tax benefits are no longer calculated due to the adoption of the ASU related to stock compensation (see Note 2), as all tax benefits are recognized in net income.

Weighted Average Assumptions Used to Value Option Grants

	Six months ended June 30,
	2016		2015
Risk-free interest rate (%)		1.39		1.52
Expected option life (years)		5.20		5.10
Expected volatility (%)		21.63		22.27
Expected dividend yield (%)		0.70		0.62