Significant Accounting Policies (Tables)

6 Months Ended

Jun. 30, 2017

Significant Accounting Policies [Abstract]

Changes in Accumulated Other Comprehensive Income (Loss)

We include unrealized gains and losses on investments, net of taxes, in accumulated other comprehensive income (loss) along with adjustments we make to reclassify realized gains and losses on investments from other accumulated comprehensive income (loss) to our condensed consolidated statement of operations. The following table summarizes changes in accumulated other comprehensive income (loss) for the three and six months ended June 30, 2017 and 2016 (in thousands):

	Three Months Ended June 30,						Six Months Ended June 30,
	2017			2016			2017			2016
Beginning balance accumulated other comprehensive loss	$	(30,460	)	$	(16,115	)	$	(30,358	)	$	(13,565	)
Unrealized gains (losses) on securities (1)		130			(10,738	)		396			(13,288	)
Amounts reclassified from accumulated other comprehensive income (loss)		—			—			(374	)		—
Currency translation adjustment		(42	)		—			(36	)		—
Net current period other comprehensive income (loss)		88			(10,738	)		(14	)		(13,288	)
Ending balance accumulated other comprehensive loss	$	(30,372	)	$	(26,853	)	$	(30,372	)	$	(26,853	)

(1) There was no tax expense or benefit related to elements of other comprehensive income (loss) for the three and six months ended June 30, 2017 and 2016.

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 six months ended June 30, 2017 and 2016, we used the following weighted-average assumptions in our Black-Scholes calculations:

Employee Stock Options:

	Six Months Ended June 30,
	2017		2016
Risk-free interest rate		1.8%		1.5%
Dividend yield		0.0%		0.0%
Volatility		66.1%		58.4%
Expected life		4.5 years		4.5 years

Weighted-Average Assumptions - ESPP

ESPP:

	Six Months Ended June 30,
	2017		2016
Risk-free interest rate		0.7%		0.5%
Dividend yield		0.0%		0.0%
Volatility		66.5%		69.4%
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, 2017 and 2016 (in thousands).  Our consolidated non-cash stock-based compensation expense includes $3.9 million and $3.1 million of stock-based compensation expense for Akcea employees for the three months ended June 30, 2017 and 2016, respectively, and $7.1 million and $6.3 million of stock-based compensation expense for Akcea employees for the six months ended June 30, 2017 and 2016, respectively.

	Three Months Ended June 30,						Six Months Ended June 30,
	2017			2016			2017			2016
Research, development and patent		$	16,140		$	14,492		$	32,262		$	29,262
Selling, general and administrative			5,118			4,768			9,908			10,102
Total non-cash stock-based compensation expense		$	21,258		$	19,260		$	42,170		$	39,364