Net Income Per Share (Tables)

6 Months Ended

Jun. 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 June 30,				Six Months Ended June 30,
	2018		2017		2018		2017
Net income - basic and diluted	$	551,412	$	387,744	$	1,029,392	$	636,675
(Shares in thousands)
Weighted average shares - basic	107,800		106,034		107,724		105,804
Effect of dilutive securities:
Stock options	6,664		9,602		6,959		9,310
Restricted stock	13		501		14		493
Dilutive potential shares	6,677		10,103		6,973		9,803
Weighted average shares - diluted	114,477		116,137		114,697		115,607
Net income per share - basic	$	5.12	$	3.66	$	9.56	$	6.02
Net income per share - diluted	$	4.82	$	3.34	$	8.97	$	5.51

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 June 30,		Six Months Ended June 30,
(Shares in thousands)	2018	2017	2018	2017
Stock options	14,865	7,959	14,872	11,055
Restricted stock	60	—	57	16