Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2017

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Schedule of Stock Based Compensation Expense

Our stock based compensation expense is as follows for the years ended December 31, 2017, 2016, and 2015 (in thousands):

	Year Ended December 31,
	2017		2016			2015
Restricted stock units	$	5,301	$	4,006		$	2,408
Performance units		3,622		1,922			1,297
Restricted stock issued to directors		378		556			827
Incentive units		—		(268	)		103
Total expense	$	9,301	$	6,216		$	4,635

Summary of Restricted Stock Unit Awards Activity

A summary of restricted stock unit awards activity during the year ended December 31, 2017 is as follows:

	Number of shares			Weighted average grant date fair value		Aggregate intrinsic value (in thousands)
Total awarded and unvested, December 31, 2016		4,343,582		$	2.14	$	11,597
Granted		2,692,797			2.12
Vested		(2,914,881	)		1.65
Forfeited		(64,144	)		2.46
Total awarded and unvested, December 31, 2017		4,057,354		$	2.48	$	9,738

Summary of Performance Stock Unit Awards Activity

A summary of performance stock unit awards activity during the year ended December 31, 2017 is as follows:

	Number of shares			Weighted average grant date fair value		Aggregate intrinsic value (in thousands)
Total awarded and unvested, December 31, 2016		1,928,002		$	3.31	$	5,148
Granted		2,564,523			1.94
Vested		(448,018	)		8.77
Forfeited		(78,130	)		2.75
Total awarded and unvested, December 31, 2017		3,966,377		$	1.82	$	11,257

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 years ended December 31, 2017, 2016, and 2015:

	Year Ended December 31,
	2017			2016			2015
Volatility		50.41	%		49.84	%		44.25	%
Risk-free interest rate		1.34	%		0.96	%		0.94	%