Unaudited Condensed Consolidated Statements of Changes in Equity and Redeemable Noncontrolling Interest - USD ($) $ in Thousands	Total	Total Stockholders' Equity	Common Stock	Additional Paid-in Capital	Accumulated Deficit	Treasury Stock	Accumulated Other Comprehensive Income (Loss)	Noncontrolling interest	Redeemable Noncontrolling Interest
Beginning balance (in shares) at Dec. 31, 2017			73,822,001
Beginning balance at Dec. 31, 2017	$ 264,842	$ 260,831	$ 386	$ 490,200	$ (224,047)	$ (5,656)	$ (52)	$ 4,011	$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation	3,122	3,122		3,122
Issuance of common stock through vesting of restricted stock units and option exercises (in shares)			246,130
Issuance of common stock through vesting of restricted stock units and option exercises	41	41	$ 2	39
Employee stock purchase plan (in shares)			196,360
Employee stock purchase plan	919	919	$ 1	918
Tax withholding related to vesting of restricted stock units	(118)	(118)		(118)
Currency translation adjustment	(113)	(63)					(63)	(50)
Other	(4)	(4)			(1)		(3)
Net Income (loss)	(2,576)	(2,058)			(2,058)			(518)
Ending balance (in shares) at Mar. 31, 2018			74,264,491
Ending balance at Mar. 31, 2018	266,113	262,670	$ 389	494,161	(226,106)	(5,656)	(118)	3,443	0
Beginning balance (in shares) at Dec. 31, 2017			73,822,001
Beginning balance at Dec. 31, 2017	264,842	260,831	$ 386	490,200	(224,047)	(5,656)	(52)	4,011	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Currency translation adjustment	(815)
Unrealized gain (loss) on derivative instrument	0
Ending balance (in shares) at Sep. 30, 2018			75,029,010
Ending balance at Sep. 30, 2018	288,592	283,352	$ 393	499,984	(210,866)	(5,656)	(503)	5,240	0
Beginning balance (in shares) at Dec. 31, 2017			73,822,001
Beginning balance at Dec. 31, 2017	$ 264,842	260,831	$ 386	490,200	(224,047)	(5,656)	(52)	4,011	0
Ending balance (in shares) at Dec. 31, 2018	75,375,341		75,375,341
Ending balance at Dec. 31, 2018	$ 302,485	297,952	$ 396	502,003	(196,959)	(5,656)	(1,832)	4,533	0
Beginning balance (in shares) at Mar. 31, 2018			74,264,491
Beginning balance at Mar. 31, 2018	266,113	262,670	$ 389	494,161	(226,106)	(5,656)	(118)	3,443	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation	2,712	2,712		2,712
Issuance of common stock through vesting of restricted stock units and option exercises (in shares)			376,513
Issuance of common stock through vesting of restricted stock units and option exercises	0		$ 2	(2)
Employee stock purchase plan	49	49		49
Tax withholding related to vesting of restricted stock units	(323)	(323)		(323)
Investment by noncontrolling interests	3,402							3,402
Currency translation adjustment	(395)	(216)					(216)	(179)
Net Income (loss)	4,612	5,628			5,628			(1,016)
Ending balance (in shares) at Jun. 30, 2018			74,641,004
Ending balance at Jun. 30, 2018	276,170	270,520	$ 391	496,597	(220,478)	(5,656)	(334)	5,650	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation	2,740	2,740		2,740
Issuance of common stock through vesting of restricted stock units and option exercises (in shares)			215,668
Issuance of common stock through vesting of restricted stock units and option exercises	37	37	$ 1	36
Employee stock purchase plan (in shares)			172,338
Employee stock purchase plan	972	972	$ 1	971
Tax withholding related to vesting of restricted stock units	(360)	(360)		(360)
Currency translation adjustment	(306)	(168)					(168)	(138)
Unrealized gain (loss) on derivative instrument	0
Other	1	1			2		(1)
Net Income (loss)	9,338	9,610			9,610			(272)
Ending balance (in shares) at Sep. 30, 2018			75,029,010
Ending balance at Sep. 30, 2018	$ 288,592	283,352	$ 393	499,984	(210,866)	(5,656)	(503)	5,240	0
Beginning balance (in shares) at Dec. 31, 2018	75,375,341		75,375,341
Beginning balance at Dec. 31, 2018	$ 302,485	297,952	$ 396	502,003	(196,959)	(5,656)	(1,832)	4,533	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation	2,743	2,743		2,743
Issuance of common stock through vesting of restricted stock units and option exercises (in shares)			264,364
Issuance of common stock through vesting of restricted stock units and option exercises	47	47	$ 2	45
Employee stock purchase plan (in shares)			267,688
Employee stock purchase plan	1,660	1,660	$ 1	1,659
Tax withholding related to vesting of restricted stock units	(291)	(291)		(291)
Currency translation adjustment	366	340					340	26
Unrealized gain (loss) on derivative instrument	(742)	(742)					(742)
Net Income (loss)	5,328	5,666			5,666			(338)
Ending balance (in shares) at Mar. 31, 2019			75,907,393
Ending balance at Mar. 31, 2019	$ 311,596	307,375	$ 399	506,159	(191,293)	(5,656)	(2,234)	4,221	0
Beginning balance (in shares) at Dec. 31, 2018	75,375,341		75,375,341
Beginning balance at Dec. 31, 2018	$ 302,485	297,952	$ 396	502,003	(196,959)	(5,656)	(1,832)	4,533	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Currency translation adjustment	194
Unrealized gain (loss) on derivative instrument	$ (651)
Ending balance (in shares) at Sep. 30, 2019	73,556,663		73,556,663
Ending balance at Sep. 30, 2019	$ 317,942	315,264	$ 404	511,857	(178,313)	(16,680)	(2,004)	2,678	15,007
Beginning balance (in shares) at Mar. 31, 2019			75,907,393
Beginning balance at Mar. 31, 2019	311,596	307,375	$ 399	506,159	(191,293)	(5,656)	(2,234)	4,221	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation	2,965	2,965		2,965
Issuance of common stock through vesting of restricted stock units and option exercises (in shares)			393,994
Issuance of common stock through vesting of restricted stock units and option exercises	28	28	$ 2	26
Employee stock purchase plan	335	335		335
Tax withholding related to vesting of restricted stock units	(844)	(844)		(844)
Fair value of redeemable noncontrolling interest resulting from business combination	0								16,444
Currency translation adjustment	414	463					463	(49)	(9)
Unrealized gain (loss) on derivative instrument	(124)	(124)					(124)
Other	(9)	(9)		(11)	1		1
Net Income (loss)	3,481	4,295			4,295			(814)	(1,313)
Ending balance (in shares) at Jun. 30, 2019			76,301,387
Ending balance at Jun. 30, 2019	317,842	314,484	$ 401	508,630	(186,997)	(5,656)	(1,894)	3,358	15,122
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation	2,143	2,143		2,143
Issuance of common stock through vesting of restricted stock units and option exercises (in shares)			156,456
Issuance of common stock through vesting of restricted stock units and option exercises	24	24	$ 1	23
Employee stock purchase plan (in shares)			303,282
Employee stock purchase plan	$ 1,235	1,235	$ 2	1,233
Repurchases of Common Stock (in shares)	(3,204,462)		(3,204,462)
Repurchases of Common Stock	$ (11,024)	(11,024)				(11,024)
Tax withholding related to vesting of restricted stock units	(172)	(172)		(172)
Currency translation adjustment	(577)
Currency translation adjustment	(447)	(325)					(325)	(122)	(130)
Unrealized gain (loss) on derivative instrument	215	215					215
Other									(1)
Net Income (loss)	$ 8,126	8,684			8,684			(558)	16
Ending balance (in shares) at Sep. 30, 2019	73,556,663		73,556,663
Ending balance at Sep. 30, 2019	$ 317,942	$ 315,264	$ 404	$ 511,857	$ (178,313)	$ (16,680)	$ (2,004)	$ 2,678	$ 15,007