Significant Accounting Policies (Tables)

6 Months Ended

Jun. 30, 2015

Significant Accounting Policies [Abstract]

Diluted common equivalent shares

For the three and six months ended June 30, 2015, we had net income. As a result, we computed diluted net income per share using the weighted-average number of common shares and dilutive common equivalent shares outstanding during those periods. Diluted common equivalent shares for the three and six months ended June 30, 2015 consisted of the following (in thousands):

Three Months Ended June 30, 2015	Income (Numerator)		Shares (Denominator)		Per-Share Amount
Income available to common shareholders	$	35,648		119,742	$	0.30
Effect of diluted securities:
Shares issuable upon exercise of stock options				3,974
Shares issuable upon restricted stock award issuance				376
Shares issuable related to our ESPP				4
Shares issuable related to our 2¾ percent notes		1,047		3,683
Income available to common shareholders, plus assumed conversions	$	36,695		127,779	$	0.29

Six Months Ended June 30, 2015	Income (Numerator)		Shares (Denominator)		Per-Share Amount
Income available to common shareholders	$	18,931		119,348	$	0.16
Effect of diluted securities:
Shares issuable upon exercise of stock options				4,310
Shares issuable upon restricted stock award issuance				399
Shares issuable related to our ESPP				4
Shares issuable related to our 2¾ percent notes		—		—
Income available to common shareholders, plus assumed conversions	$	18,931		124,061	$	0.15

Changes in accumulated other comprehensive income

Accumulated other comprehensive income is comprised of unrealized gains and losses on investments, net of taxes, and adjustments we made to reclassify realized gains and losses on investments from other accumulated comprehensive income to our condensed consolidated statement of operations. The following table summarizes changes in accumulated other comprehensive income for the three and six months ended June 30, 2015 and 2014 (in thousands):

	Three Months Ended June 30,						Six Months Ended  June 30,
	2015			2014			2015			2014
Beginning balance accumulated other comprehensive income	$	47,114		$	29,000		$	39,747		$	21,080
Unrealized (losses) gains on securities, net of tax (1)		(28,703	)		(4,456	)		(21,336	)		3,806
Amounts reclassified from accumulated other comprehensive income (2)		—			175			—			(167	)
Net current period other comprehensive (loss) income		(28,703	)		(4,281	)		(21,336	)		3,639
Ending balance accumulated other comprehensive income	$	18,411		$	24,719		$	18,411		$	24,719

(1) Other comprehensive loss for the three months ended June 30, 2015 includes income tax benefit of $5.1 million, compared to $2.9 million for the same period in 2014. For the six months ended June 30, 2014 other comprehensive income includes income tax expense of $2.5 million. There was no tax expense or benefit for the six months ended June 30, 2015.

(2) Included in gain on investments, net on our condensed consolidated statement of operations.

Weighted-average assumptions - Employee stock options

We use the Black-Scholes model to estimate the fair value of stock options granted and stock purchase rights under our ESPP. The expected term of stock options granted represents the period of time that we expect them to be outstanding. We estimate the expected term of options granted based on historical exercise patterns. For the six months ended June 30, 2015 and 2014, we used the following weighted-average assumptions in our Black-Scholes calculations:

Employee Stock Options:

	Six Months Ended June 30,
	2015		2014
Risk-free interest rate		1.5%		1.6%
Dividend yield		0.0%		0.0%
Volatility		53.6%		50.6%
Expected life		4.5 years		4.6 years

Weighted-average assumptions - ESPP

ESPP:

	Six Months Ended June 30,
	2015		2014
Risk-free interest rate		0.1%		0.1%
Dividend yield		0.0%		0.0%
Volatility		56.2%		59.0%
Expected life		6 months		6 months

Stock-based compensation expense

The following table summarizes stock-based compensation expense for the three and six months ended June 30, 2015 and 2014 (in thousands), which was allocated as follows:

	Three Months Ended  June 30,						Six Months Ended June 30,
	2015			2014			2015			2014
Research, development and patent expenses		$	10,465		$	6,401		$	20,951		$	12,274
General and administrative			3,140			1,307			5,959			2,503
Total		$	13,605		$	7,708		$	26,910		$	14,777