Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2017

Summary of Stock-Based Compensation Expense

The following table summarizes the Company’s stock-based compensation expense (in thousands):

	Year Ended December 31,
	2017		2016		2015
Time-based restricted stock and time-based restricted stock units	$	1,992	$	2,281	$	2,704
Performance-based restricted stock and performance-based restricted stock units		2,805		2,210		1,562
Stock appreciation rights		251		184		525
Employee stock purchase plan		139		113		70
Total stock-based compensation	$	5,187	$	4,788	$	4,861

Summary of Assumptions Used to Estimate Fair Value of Each SAR

The fair value of each SAR is estimated on the date of grant using a Black-Scholes option-pricing model. There were no SARs issued in the year ended December 31, 2016. For SARs issued in the years ended December 31, 2017 and 2015, respectively, the assumptions shown in the following table were used:

	December 31,
	2017			2015
Dividend yield		0	%		0	%
Average risk-free interest rate		2.0	%		1.6	%
Expected term (years)		5			5
Expected volatility		42.3	%		42.9	%

SAR Activity

SAR activity under the Plan and all predecessor stock incentive plans is as follows:

	SARs			Weighted-Average Grant Price Per Share		Weighted- Average Remaining Contractual Life (Years)		Aggregate Intrinsic Value as of December 31, 2017
Outstanding at December 31, 2014		515,830		$	13.98
Granted		15,585		$	41.19
Exercised		(263,626	)	$	13.86
Canceled		(5,712	)	$	21.94
Outstanding at December 31, 2015		262,077		$	13.13
Granted		—		$	—
Exercised		(124,352	)	$	11.09
Canceled		—		$	—
Outstanding at December 31, 2016		137,725		$	19.57
Granted		18,739		$	70.75
Exercised		(17,406	)	$	16.13
Canceled		—		$	—
Outstanding at December 31, 2017		139,058		$	26.89		5.3	$	11,333,033
Vested at December 31, 2017		139,058		$	26.89		5.3	$	11,333,033
Exercisable at December 31, 2017		115,191		$	19.12		4.6	$	10,282,908

Time-Based Restricted Stock and Time-Based Restricted Stock Units [Member]

Restricted Stock Activity

Time-based restricted stock and restricted stock unit activity under the Plan and all predecessor stock incentive plans is as follows:

	Time-based Restricted Stock and Restricted Stock Unit			Weighted-Average Grant Price Per Share
Nonvested at December 31, 2014		329,562		$	18.89
Granted		57,598		$	43.81
Vested		(230,704	)	$	42.37
Forfeited		(48,549	)	$	20.20
Nonvested at December 31, 2015		107,907		$	29.43
Granted		57,874		$	37.64
Vested		(43,848	)	$	42.34
Forfeited		(133	)	$	43.89
Nonvested at December 31, 2016		121,800		$	31.59
Granted		36,201		$	72.54
Vested		(81,186	)	$	28.90
Forfeited		(256	)	$	37.36
Nonvested at December 31, 2017		76,559		$	53.79

Performance-Based Restricted Stock and Performance-Based Restricted Stock Units [Member]

Restricted Stock Activity

Performance-based restricted stock activity under the Plan is as follows:

	Performance-based Restricted Stock and Performance-based Restricted Stock Units			Weighted-Average Grant Price Per Share
Nonvested at December 31, 2014		42,676		$	33.72
Granted		34,638		$	43.89
Vested		(35,679	)	$	41.91
Forfeited		(12,538	)	$	38.12
Nonvested at December 31, 2015		29,097		$	39.38
Granted		44,925		$	35.83
Vested		(14,949	)	$	35.71
Forfeited		(657	)	$	33.72
Nonvested at December 31, 2016		58,416		$	36.63
Granted		43,307		$	57.54
Vested		(43,394	)	$	37.27
Forfeited		—		$	—
Nonvested at December 31, 2017		58,329		$	51.69