Revision of Prior Period Financial Statements - Revised Consolidated Balance Sheet Amounts (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Accounts receivable, net of allowance for doubtful accounts of $3,830 and $4,880, respectively	$ 202,406	$ 191,145	$ 188,614	$ 184,277	$ 193,186	$ 188,605	$ 185,290	$ 183,084	$ 205,448
Unbilled revenue	48,396	65,370	60,554	50,940	46,252	59,734	47,678	47,442
Inventories	34,977	63,996	51,172	46,624	55,715
Prepaid expenses	10,680	13,247	14,406	13,518	16,256
Other current assets	7,301	13,479	28,915	36,394	10,733	43,323	26,656	34,109	38,200
Total current assets	374,665	425,042	377,660	357,604	372,639	397,915	349,255	366,518	383,485
Total assets	629,283	679,471	630,267	598,988	621,729	661,735	644,617	634,195	650,035
Property and equipment, net	37,224	36,837			82,933
Accounts payable	142,136	168,423	139,591	148,532	158,028	161,140	122,336	120,197	141,108
Accrued expenses	50,975	43,933	37,788	31,591	35,698	36,175	35,022	40,717	35,026
Deferred revenue	9,568	18,364	21,497		17,614
Other current liabilities	35,665	33,339	35,776	33,695	28,190	23,504	24,672	25,942	25,927
Total current liabilities	246,437	274,894	392,327	373,686	382,266	251,523	338,590	218,380	219,681
Deferred income taxes	8,053	7,684	7,722	7,695	7,605	11,735	11,828	11,800	11,634
Total liabilities	451,031	498,978	448,659	418,411	440,774	451,835	388,640	356,353	367,112
Accumulated other comprehensive loss	(22,449)	(25,083)	(23,337)	(23,599)	(24,311)
Retained earnings	36,855	43,335	44,400	44,907	46,771	76,160	121,280	121,581	122,820
Total stockholders' equity	178,252	180,493	181,608	180,577	180,955	209,900	255,977	277,842	282,923	$ 262,161
Total liabilities and stockholders' equity	$ 629,283	679,471	630,267	598,988	621,729	661,735	644,617	634,195	650,035
As Reported
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Accounts receivable, net of allowance for doubtful accounts of $3,830 and $4,880, respectively		190,992	188,687	184,359	193,253	188,744	185,222	183,012	205,386
Unbilled revenue		65,584	60,911	51,166	46,474	59,961	47,906	47,685
Inventories		64,136	51,553	46,927	56,001
Prepaid expenses		13,973	15,132	14,245	16,982
Other current assets		13,271	28,707	36,188	10,379	43,005	26,296	33,716	37,865
Total current assets		425,761	378,989	358,736	373,586	397,963	349,055	366,296	383,088
Total assets		680,067	631,596	600,120	622,676	661,783	644,417	633,973	649,638
Property and equipment, net		36,714
Accounts payable		169,173	140,492	149,813	158,449	161,389	122,452	120,260	141,164
Accrued expenses		44,096	37,446	31,339	35,474	35,539	34,386	40,081	34,391
Deferred revenue		18,526	21,532
Other current liabilities		32,325	34,877	31,493	26,231	21,535	22,770	24,073	24,078
Total current liabilities		274,955	392,022	372,513	380,504	249,167	336,168	215,938	217,253
Deferred income taxes		8,257	8,295	8,268	8,178	12,143	12,236	12,208	12,043
Total liabilities		499,612	448,927	417,811	439,585	449,887	386,626	354,319	365,093
Accumulated other comprehensive loss		(25,045)	(23,309)	(23,562)	(24,309)
Retained earnings		43,259	45,433	46,602	48,905	78,156	123,094	123,393	124,442
Total stockholders' equity		180,455	182,669	182,309	183,091	211,896	257,791	279,654	284,545
Total liabilities and stockholders' equity		680,067	631,596	600,120	622,676	661,783	644,417	633,973	649,638
Adjustments
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Accounts receivable, net of allowance for doubtful accounts of $3,830 and $4,880, respectively		153	(73)	(82)	(67)	(139)	68	72	62
Unbilled revenue		(214)	(357)	(226)	(222)	(227)	(228)	(243)
Inventories		(140)	(381)	(303)	(286)
Prepaid expenses		(726)	(726)	(727)	(726)
Other current assets		208	208	206	354	318	360	393	335
Total current assets		(719)	(1,329)	(1,132)	(947)	(48)	200	222	397
Total assets		(596)	(1,329)	(1,132)	(947)	(48)	200	222	397
Property and equipment, net		123
Accounts payable		(750)	(901)	(1,281)	(421)	(249)	(116)	(63)	(56)
Accrued expenses		(163)	342	252	224	636	636	636	635
Deferred revenue		(162)	(35)
Other current liabilities		1,014	899	2,202	1,959	1,969	1,902	1,869	1,849
Total current liabilities		(61)	305	1,173	1,762	2,356	2,422	2,442	2,428
Deferred income taxes		(573)	(573)	(573)	(573)	(408)	(408)	(408)	(409)
Total liabilities		(634)	(268)	600	1,189	1,948	2,014	2,034	2,019
Accumulated other comprehensive loss		(38)	(28)	(37)	(2)
Retained earnings		76	(1,033)	(1,695)	(2,134)	(1,996)	(1,814)	(1,812)	(1,622)
Total stockholders' equity		38	(1,061)	(1,732)	(2,136)	(1,996)	(1,814)	(1,812)	(1,622)
Total liabilities and stockholders' equity		$ (596)	$ (1,329)	$ (1,132)	$ (947)	$ (48)	$ 200	$ 222	$ 397