Significant Accounting Policies (Tables)

3 Months Ended

Mar. 31, 2016

Significant Accounting Policies [Abstract]

Changes in Accumulated Other Comprehensive Income (Loss)

Accumulated other comprehensive income (loss) 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 (loss) for the three months ended March 31, 2016 and 2015 (in thousands):

	Three Months Ended March 31,
	2016			2015
Beginning balance accumulated other comprehensive income (loss)	$	(13,565	)	$	39,747
Other comprehensive income (loss) before reclassifications, net of tax (1)		(2,550	)		7,367
Net current period other comprehensive income (loss)		(2,550	)		7,367
Ending balance accumulated other comprehensive income (loss)	$	(16,115	)	$	47,114

(1) Other comprehensive income from the three months ended March 31, 2015 includes income tax expense of $5.1 million. There was no tax benefit for other comprehensive loss for the three months ended March 31, 2016.

Significant Accounting Policies [Abstract]

Weighted-Average Assumptions - ESPP

ESPP:

	Three Months Ended March 31,
	2016		2015
Risk-free interest rate		0.5%		0.1%
Dividend yield		0.0%		0.0%
Volatility		69.4%		56.2%
Expected life		6 months		6 months

Stock-Based Compensation Expense

The following table summarizes stock-based compensation expense for the three months ended March 31, 2016 and 2015 (in thousands). Our consolidated non-cash stock-based compensation expense includes $3.2 million and $0.6 million of stock-based compensation expense for Akcea employees for the three months ended March 31, 2016 and 2015.

	Three Months Ended  March 31,
	2016			2015
Research, development and patent expenses		$	14,770		$	10,486
General and administrative			5,333			2,819
Total		$	20,103		$	13,305

Employee Stock Options [Member]

Significant Accounting Policies [Abstract]

Weighted-Average Assumptions

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, 2016 and 2015, we used the following weighted-average assumptions in our Black-Scholes calculations:

Employee Stock Options:

	Three Months Ended March 31,
	2016		2015
Risk-free interest rate		1.5%		1.5%
Dividend yield		0.0%		0.0%
Volatility		57.9%		53.5%
Expected life		4.5 years		4.5 years