Significant Accounting Policies (Tables)

3 Months Ended

Mar. 31, 2015

Significant Accounting Policies [Abstract]

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

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 months ended March 31, 2015 and 2014 (in thousands):

	Three Months Ended March 31,
	2015		2014
Beginning balance accumulated other comprehensive income	$	39,747	$	21,080
Other comprehensive income before reclassifications, net of tax (1)		7,367		8,261
Amounts reclassified from accumulated other comprehensive income (2)		—		(341	)
Net current period other comprehensive income		7,367		7,920
Ending balance accumulated other comprehensive income	$	47,114	$	29,000

(1) Other comprehensive income from the three months ended March 31, 2015 includes income tax expense of $5.1 million, compared to $5.4 million for the three months ended March 31, 2014.

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

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Schedule of weighted-average assumptions used for valuation of ESPP

ESPP:

	Three Months Ended March 31,
	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

Schedule of stock-based compensation expense

The following table summarizes stock-based compensation expense for the three months ended March 31, 2015 and 2014 (in thousands), which was allocated as follows:

	Three Months Ended March 31,
	2015			2014
Research, development and patent expenses		$	10,486		$	5,873
General and administrative			2,819			1,196
Total		$	13,305		$	7,069

Employee Stock Options [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

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 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 three months ended March 31, 2015 and 2014, we used the following weighted-average assumptions in our Black-Scholes calculations:

Employee Stock Options:

	Three Months Ended March 31,
	2015		2014
Risk-free interest rate		1.5%		1.6%
Dividend yield		0.0%		0.0%
Volatility		53.5%		50.5%
Expected life		4.5 years		4.6 years

Board of Director Stock Option [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

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

Board of Director Stock Options:

	Three Months Ended March 31, 2014
Risk-free interest rate		2.3	%
Dividend yield		0.0	%
Volatility		53.3	%
Expected life	7.1 years