Stockholders' Equity (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Jan. 01, 2018	Dec. 31, 2017	Jan. 01, 2017
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at December 31, 2017			$ 188,054
Net income	$ 3,575	$ 5,863	6,207	$ 9,949
Cumulative effect adjustment of adopting ASU 2014-09					$ 400		$ (396)
Adjusted balance at December 31, 2017						$ 187,658
Foreign currency translation adjustment			(3,205)
Repurchases of common stock			(7,294)
Stock-based compensation expense			1,097
Issuance of stock for employer contributions to retirement plan			1,437
Other			(80)
Ending Balance	186,084		$ 186,084
Stock repurchased during period, shares			313,000	101,000
Stock repurchased during period, value			$ 7,300	$ 2,400
Stock repurchase program, remaining authorized repurchase amount	4,500		4,500
Common stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at December 31, 2017			172
Adjusted balance at December 31, 2017						172
Ending Balance	172		172
Additional paid-in capital
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at December 31, 2017			107,256
Cumulative effect adjustment of adopting ASU 2014-09							0
Adjusted balance at December 31, 2017						107,256
Stock-based compensation expense			1,097
Issuance of stock for employer contributions to retirement plan			(88)
Other			(893)
Ending Balance	107,372		107,372
Retained earnings
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at December 31, 2017			106,599
Cumulative effect adjustment of adopting ASU 2014-09							$ (396)
Adjusted balance at December 31, 2017						106,203
Ending Balance	112,410		112,410
Treasury stock at cost
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at December 31, 2017			(11,118)
Adjusted balance at December 31, 2017						(11,118)
Repurchases of common stock			(7,294)
Issuance of stock for employer contributions to retirement plan			1,525
Other			813
Ending Balance	(16,074)		(16,074)
Accumulated other comprehensive loss
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at December 31, 2017			(14,855)
Adjusted balance at December 31, 2017						$ (14,855)
Foreign currency translation adjustment			(3,205)
Ending Balance	$ (17,796)		(17,796)
Interest Rate Cap
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Change in fair value of interest rate derivative instrument, net of tax			205
Interest Rate Cap | Accumulated other comprehensive loss
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Change in fair value of interest rate derivative instrument, net of tax			205
Interest Rate Swap
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Change in fair value of interest rate derivative instrument, net of tax			59
Interest Rate Swap | Accumulated other comprehensive loss
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Change in fair value of interest rate derivative instrument, net of tax			$ 59