Consolidated Statements of Changes in Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Cumulative Effect, Period of Adoption, Adjustment [Member]	Common Stock [Member] Class A Common Stock [Member]	Common Stock [Member] Class B Common Stock [Member]	Additional Paid-In Capital [Member]	Accumulated Deficit [Member]	Accumulated Deficit [Member] Cumulative Effect, Period of Adoption, Adjustment [Member]	Accumulated Other Comprehensive Loss [Member]
Beginning balance at Dec. 31, 2018	$ 293,686		$ 4	$ 3	$ 379,832	$ (74,863)		$ (11,290)
Beginning balance (in shares) at Dec. 31, 2018			38,349	32,171
Net income (loss)	13,019					13,019
Exercise of stock options	458				458
Exercise of stock options (in shares)			397
Vesting of restricted stock (in shares)			14
Stock-based compensation	869				869
Foreign currency translation, net of tax	337							337
Retirement related benefit plans, net of tax	228							228
Ending balance at Mar. 31, 2019	308,597		$ 4	$ 3	381,159	(61,844)		(10,725)
Ending balance (in shares) at Mar. 31, 2019			38,760	32,171
Beginning balance at Dec. 31, 2018	293,686		$ 4	$ 3	379,832	(74,863)		(11,290)
Beginning balance (in shares) at Dec. 31, 2018			38,349	32,171
Net income (loss)	(6,040)
Foreign currency translation, net of tax	(1,046)
Retirement related benefit plans, net of tax	376
Ending balance at Sep. 30, 2019	343,341		$ 4	$ 3	436,197	(80,903)		(11,960)
Ending balance (in shares) at Sep. 30, 2019			40,354	31,391
Beginning balance at Mar. 31, 2019	308,597		$ 4	$ 3	381,159	(61,844)		(10,725)
Beginning balance (in shares) at Mar. 31, 2019			38,760	32,171
Net income (loss)	(3,120)					(3,120)
Equity component of convertible senior notes,net of issuance costs	50,009				50,009
Exercise of stock options	812				812
Exercise of stock options (in shares)			608
Vesting of restricted stock (in shares)			34
Conversion from Class B to Class A common stock			270	(270)
Stock-based compensation	1,922				1,922
Foreign currency translation, net of tax	1,605							1,605
Retirement related benefit plans, net of tax	16							16
Ending balance at Jun. 30, 2019	359,841		$ 4	$ 3	433,902	(64,964)		(9,104)
Ending balance (in shares) at Jun. 30, 2019			39,672	31,901
Net income (loss)	(15,939)					(15,939)
Exercise of stock options	169				169
Exercise of stock options (in shares)			165
Vesting of restricted stock (in shares)			7
Conversion from Class B to Class A common stock			510	(510)
Stock-based compensation	2,126				2,126
Foreign currency translation, net of tax	(2,988)							(2,988)
Retirement related benefit plans, net of tax	132							132
Ending balance at Sep. 30, 2019	343,341		$ 4	$ 3	436,197	(80,903)		(11,960)
Ending balance (in shares) at Sep. 30, 2019			40,354	31,391
Beginning balance at Dec. 31, 2019	354,707	$ (388)	$ 4	$ 3	446,633	(82,405)	$ (388)	(9,528)
Beginning balance (in shares) at Dec. 31, 2019			41,271	31,131
Net income (loss)	6,030					6,030
Exercise of stock options	194				194
Exercise of stock options (in shares)			285
Vesting of restricted stock (in shares)			143
Conversion from Class B to Class A common stock			80	(80)
Stock-based compensation	3,043				3,043
Foreign currency translation, net of tax	(7,578)							(7,578)
Retirement related benefit plans, net of tax	137							137
Ending balance at Mar. 31, 2020	356,145		$ 4	$ 3	449,870	(76,763)		(16,969)
Ending balance (in shares) at Mar. 31, 2020			41,779	31,051
Beginning balance at Dec. 31, 2019	354,707	$ (388)	$ 4	$ 3	446,633	(82,405)	$ (388)	(9,528)
Beginning balance (in shares) at Dec. 31, 2019			41,271	31,131
Net income (loss)	(12,698)
Foreign currency translation, net of tax	(446)
Retirement related benefit plans, net of tax	110
Ending balance at Sep. 30, 2020	359,455		$ 4	$ 3	464,803	(95,491)		(9,864)
Ending balance (in shares) at Sep. 30, 2020			42,870	30,591
Beginning balance at Mar. 31, 2020	356,145		$ 4	$ 3	449,870	(76,763)		(16,969)
Beginning balance (in shares) at Mar. 31, 2020			41,779	31,051
Net income (loss)	(10,223)					(10,223)
Exercise of stock options	283				283
Exercise of stock options (in shares)			197
Vesting of restricted stock (in shares)			52
Conversion from Class B to Class A common stock			80	(80)
Stock-based compensation	4,586				4,586
Reclassification of mezzanine equity topermanent equity	1,568				1,568
Foreign currency translation, net of tax	2,560							2,560
Retirement related benefit plans, net of tax	31							31
Ending balance at Jun. 30, 2020	354,950		$ 4	$ 3	456,307	(86,986)		(14,378)
Ending balance (in shares) at Jun. 30, 2020			42,108	30,971
Net income (loss)	(8,505)					(8,505)
Issuance of common stock for acquisitions	1,638				1,638
Issuance of common stock for acquisitions (in shares)			40
Exercise of stock options	618				618
Exercise of stock options (in shares)			328
Vesting of restricted stock (in shares)			14
Conversion from Class B to Class A common stock			380	(380)
Stock-based compensation	6,240				6,240
Foreign currency translation, net of tax	4,572							4,572
Retirement related benefit plans, net of tax	(58)							(58)
Ending balance at Sep. 30, 2020	$ 359,455		$ 4	$ 3	$ 464,803	$ (95,491)		$ (9,864)
Ending balance (in shares) at Sep. 30, 2020			42,870	30,591