Stockholders' Equity (Tables)

12 Months Ended

Dec. 31, 2017

Stockholders' Equity [Abstract]

Stock Option Activity

The following table summarizes the stock option activity for the year ended December 31, 2017 (in thousands, except per share and contractual life data):

	Number of Shares			Weighted Average Exercise Price Per Share		Average Remaining Contractual Term (Years)		Aggregate Intrinsic Value
Outstanding at December 31, 2016		9,178		$	40.48
Granted		3,274		$	47.76
Exercised		(1,345	)	$	15.74
Cancelled/forfeited/expired		(1,710	)	$	51.71
Outstanding at December 31, 2017		9,397		$	44.52		4.42		$	92,288
Exercisable at December 31, 2017		5,182		$	39.10		3.33		$	80,167

RSU Activity

The following table summarizes the RSU activity for the year ended December 31, 2017 (in thousands, except per share data):

	Number of Shares			Weighted Average Grant Date Fair Value Per Share
Non-vested at December 31, 2016		778		$	47.68
Granted		420		$	48.88
Vested		(296	)	$	43.79
Cancelled/forfeited		(39	)	$	48.90
Non-vested at December 31, 2017		863		$	49.55

Stock-Based Compensation Expense

The following table summarizes stock-based compensation expense for the years ended December 31, 2017, 2016 and 2015 (in thousands), which was allocated as follows and includes $17.5 million, $10.1 million and $6.5 million of stock-based compensation expense for Akcea employees in 2017, 2016 and 2015, respectively:

	Years Ended December 31,
	2017			2016			2015
Research, development and patent		$	64,521		$	55,099		$	43,638
Selling, general and administrative			21,454			17,009			15,676
Total		$	85,975		$	72,108		$	59,314

Weighted-Average Assumptions for Stock Options

For the years ended December 31, 2017, 2016 and 2015, we used the following weighted-average assumptions in our Black-Scholes calculations:

Employee Stock Options:

	December 31,
	2017			2016			2015
Risk-free interest rate		1.8	%		1.5	%		1.5	%
Dividend yield		0.0	%		0.0	%		0.0	%
Volatility		65.9	%		58.7	%		53.8	%
Expected life	4.5 years			4.5 years			4.5 years

Board of Director Stock Options:

	December 31,
	2017			2016			2015
Risk-free interest rate		2.2	%		1.3	%		2.1	%
Dividend yield		0.0	%		0.0	%		0.0	%
Volatility		61.2	%		53.1	%		52.2	%
Expected life	6.6 years			6.5 years			6.9 years

Weighted-Average Assumptions for ESPP

ESPP:

	December 31,
	2017			2016			2015
Risk-free interest rate		0.8	%		0.4	%		0.1	%
Dividend yield		0.0	%		0.0	%		0.0	%
Volatility		59.9	%		86.4	%		51.7	%
Expected life	6 months			6 months			6 months