Stock-Based Compensation (Tables)

6 Months Ended

Jun. 30, 2018

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Schedule of Stock Based Compensation Expense

Our stock-based compensation expense was as follows for the three and six months ended June 30, 2018 and 2017 (in thousands):

	Three Months Ended June 30,				Six Months Ended June 30,
	2018		2017		2018		2017
Restricted stock units	$	974	$	1,344	$	2,137	$	2,591
Performance units		910		907		1,639		1,641
Restricted stock issued to directors		95		97		184		197
Total expense	$	1,979	$	2,348	$	3,960	$	4,429

Summary of Employee Restricted Stock Unit Awards Activity

A summary of employee restricted stock unit awards activity during the six months ended June 30, 2018 is as follows:

	Number of shares			Weighted average grant date fair value		Aggregate intrinsic value (in thousands)
Total awarded and unvested, December 31, 2017		4,057,354		$	2.48	$	9,738
Granted		1,498,524			1.70
Vested		(1,862,526	)		2.88
Forfeited		(38,077	)		2.11
Total awarded and unvested, June 30, 2018		3,655,275		$	1.95	$	5,848

Summary of Performance Stock Unit Awards Activity

A summary of performance stock unit awards activity during the six months ended June 30, 2018 is as follows

	Number of shares			Weighted average grant date fair value		Aggregate intrinsic value (in thousands)
Total awarded and unvested, December 31, 2017		3,966,377		$	1.82	$	11,257
Granted		1,498,524			1.92
Vested		—			—
Forfeited		(60,127	)		1.83
Total awarded and unvested, June 30, 2018		5,404,774		$	1.84	$	3,173

Assumptions Used to Determine Fair Value of Performance Stock Units Granted

The following table presents the assumptions used to determine the fair value for performance stock units granted during the six months ended June 30, 2018 and 2017:

	Six Months Ended June 30,
	2018			2017
Volatility		89.70	%		50.41	%
Risk-free interest rate		2.37	%		1.34	%