Stockholders' Equity (Tables)

12 Months Ended

Dec. 31, 2015

Earnings Per Common Share

Schedule of components of basic and diluted earnings per share

        The components of basic and diluted earnings per share comprised the following (in thousands, except per share amounts):

	Year Ended December 31,
	2015		2014		2013
Numerator:
Net income	$	651,639	$	340,074	$	174,560
Denominator:
Weighted average outstanding shares—basic		46,000		48,176		50,076
Effect of dilutive securities(1):
Convertible notes		915		2,630		1,736
Warrants		3,009		1,910		276
Stock options and employee stock purchase plan		1,297		1,439		1,143
Weighted average shares—diluted		51,221		54,155		53,231
Earnings per common share:
Basic	$	14.17	$	7.06	$	3.49
Diluted	$	12.72	$	6.28	$	3.28
Stock options and warrants excluded from calculation(2)		3,800		9,273		11,210

(1)

Calculated using the treasury stock method.

(2)

Certain stock options and warrants have been excluded from the computation of diluted earnings per share because their impact would be anti-dilutive. Under our convertible note hedge agreement, we are entitled to receive shares required to be issued to investors upon conversion of our Convertible Notes. Since related shares used to compute dilutive earnings per share would be anti-dilutive, they have been excluded from the calculation above.

Stock Options

Stock Option Plan

Summary of assumptions to estimate the grant date fair value of stock option

	Year Ended December 31,
	2015		2014
Expected volatility		33.1%		32.6%
Risk-free interest rate		2.0%		1.7%
Expected term of options (in years)		5.8		5.0
Expected forfeiture rate		1.5%		0.0%
Expected dividend yield		0.0%		0.0%

Schedule of stock option activity

	Options			Weighted- Average Exercise Price		Weighted Average Remaining Contractual Term (in Years)		Aggregate Intrinsic Value (in 000s)
Outstanding at January 1, 2015		4,054,771		$	76.83
Granted		172,250			173.25
Exercised		(984,583	)		39.90
Forfeited		—			—
Outstanding at December 31, 2015		3,242,438		$	93.17		6.6	$	208,643
Exercisable at December 31, 2015		3,070,188		$	88.68		6.4	$	208,559
Expected to vest at December 31, 2015		169,737		$	173.53		9.5	$	73

Schedule of share-based compensation expense related to employee stock options

        Total share-based compensation expense relating to employee stock options is as follows (in thousands):

	Year Ended December 31,
	2015			2014			2013
Research and development	$	3		$	—		$	—
Selling, general and administrative		4,894			29,460			36,097
Related income tax benefit		(1,847	)		(10,429	)		(13,566	)
Share-based compensation expense, net of taxes	$	3,050		$	19,031		$	22,531

Summary of stock option exercise data

        Employee and non-employee stock option exercise data is summarized below (dollars in thousands):

	Year Ended December 31,
	2015		2014		2013
Number of options exercised		985,583		1,462,369		876,115
Cash received from options exercised	$	39,311	$	50,168	$	26,619
Total intrinsic value of options exercised	$	120,319	$	108,425	$	37,530
Tax benefits realized from options exercised	$	37,426	$	30,845	$	9,299