Significant Accounting Policies (Tables)

6 Months Ended

Jun. 30, 2014

Significant Accounting Policies [Abstract]

Changes in other accumulated other comprehensive income related to unrealized gains and losses on securities

Accumulated other comprehensive income is comprised of unrealized gains and losses on securities, net of taxes, and  adjustments we made to reclassify realized gains and losses on securities 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, 2014 and 2013 (in thousands):

	Three Months Ended June 30,					Six Months Ended June 30,
	2014			2013		2014			2013
Beginning balance accumulated other comprehensive income	$	29,000		$	17,784	$	21,080		$	12,480
Unrealized (losses) gains on securities, net of tax (1)		(4,456	)		9,202		3,806			15,669
Amounts reclassified from accumulated other comprehensive income (2)		175			-		(167	)		(1,163	)
Net current period other comprehensive income (loss)		(4,281	)		9,202		3,639			14,506
Ending balance accumulated other comprehensive income	$	24,719		$	26,986	$	24,719		$	26,986

(1) Other comprehensive income for the three and six months ended June 30, 2014 includes income tax benefit of $2.9 million and income tax expense of $2.5 million, respectively, compared to an income tax benefit of $2.9 million and $10.0 million for same periods in 2013.

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

Stock-based compensation expense

Schedule of weighted-average assumptions used for valuation of ESPP

ESPP:

	Six Months Ended June 30,
	2014			2013
Risk-free interest rate		0.1	%		0.1	%
Dividend yield		0.0	%		0.0	%
Volatility		59.0	%		61.4	%
Expected life	6 months			6 months

Schedule of stock-based compensation expense

The following table summarizes stock-based compensation expense for the three and six months ended June 30, 2014 and 2013 (in thousands), which was allocated as follows:

	Three Months Ended June 30,						Six Months Ended June 30,
	2014			2013			2014			2013
Research, development and patent expenses		$	6,401		$	2,252		$	12,274		$	4,798
General and administrative			1,307			384			2,503			707
Total		$	7,708		$	2,636		$	14,777		$	5,505

Employee Stock Options [Member]

Stock-based compensation expense

Schedule of weighted-average assumptions used for valuation of stock options

We use the Black-Scholes model to estimate the fair value of stock options granted and stock purchase rights under the 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, 2014 and 2013, we used the following weighted-average assumptions in our Black-Scholes calculations:

Employee Stock Options:

	Six Months Ended June 30,
	2014		2013
Risk-free interest rate		1.6%		1.0%
Dividend yield		0.0%		0.0%
Volatility		50.6%		51.5%
Expected life		4.6 years		5.1 years

Board of Director Stock Option [Member]

Stock-based compensation expense

Schedule of weighted-average assumptions used for valuation of stock options

Board of Director Stock Options:

	Six Months Ended June 30,
	2014			2013
Risk-free interest rate		2.3	%		2.3	%
Dividend yield		0.0	%		0.0	%
Volatility		53.3	%		52.4	%
Expected life	7.1 years			7.3 years