Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2018

Schedule of Stock Based Compensation Expense

Our stock based compensation expense is as follows for the years ended December 31, 2018, 2017, and 2016 (in thousands):

	Year Ended December 31,
	2018		2017		2016
Restricted stock units	$	4,014	$	5,301	$	4,006
Performance units		3,497		3,622		1,922
Restricted stock issued to directors		380		378		556
Incentive units		—		—		(268	)
Total expense	$	7,891	$	9,301	$	6,216

Summary of Employee Restricted Stock Unit Awards Activity

A summary of employee restricted stock unit awards activity during the year ended December 31, 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		270,490		$	37.20	$	9,738
Granted		99,901			25.50
Vested		(132,406	)		42.42
Forfeited		(4,025	)		31.30
Total awarded and unvested, December 31, 2018		233,960		$	29.27	$	3,685

Summary of Performance Stock Unit Awards Activity

A summary of performance stock unit awards activity during the year ended December 31, 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		264,425		$	27.30	$	11,257
Granted		99,901			28.80
Vested		(11,536	)		27.51
Forfeited		(6,201	)		27.61
Total awarded and unvested, December 31, 2018		346,589		$	27.68	$	716

Performance Units [Member]

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, 2018, 2017, and 2016:

	Year Ended December 31,
	2018			2017			2016
Volatility		89.70	%		50.41	%		49.84	%
Risk-free interest rate		2.37	%		1.34	%		0.96	%