Net Income Per Share (Tables)

9 Months Ended

Sep. 30, 2018

Earnings Per Share [Abstract]

Basic and Diluted Net Income (Loss) Per Share

The calculations of basic and diluted net income per share are as follows:

	Three Months Ended September 30,				Nine Months Ended September 30,
	2018		2017		2018		2017
Net income - basic and diluted	$	594,655	$	388,317	$	1,624,047	$	1,024,992
(Shares in thousands)
Weighted average shares - basic	108,033		106,706		107,828		106,108
Effect of dilutive securities:
Stock options	7,027		9,809		6,999		9,386
Restricted stock	28		513		16		500
Dilutive potential shares	7,055		10,322		7,015		9,886
Weighted average shares - diluted	115,088		117,028		114,843		115,994
Net income per share - basic	$	5.50	$	3.64	$	15.06	$	9.66
Net income per share - diluted	$	5.17	$	3.32	$	14.14	$	8.84

Antidilutive Securities

Shares which have been excluded from diluted per share amounts because their effect would have been antidilutive include the following:

	Three Months Ended September 30,		Nine Months Ended September 30,
(Shares in thousands)	2018	2017	2018	2017
Stock options	14,446	4,515	14,821	8,892
Restricted stock	—	—	57	—