Quarterly Financial Data (Unaudited) - Condensed Consolidated Statements of Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended								6 Months Ended		9 Months Ended		12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Net (loss) income	$ (7,534)	$ 7,180	$ 6,146	$ 9,986	$ 8,097	$ 11,277	$ 12,671	$ 9,444	$ 16,132	$ 22,115	$ 23,312	$ 33,392	$ 15,778	$ 41,489	$ (2,269)
Other comprehensive (loss) income:
Foreign currency translation adjustments	1,866	(3,388)	233	104	(312)	(1,529)	(5,304)	1,470	337	(3,834)	(3,051)	(5,363)	(1,185)	(5,675)	7,141
Minimum pension liability, net of tax	3,743	(2,095)	1,739	(649)	935	(1,060)	(594)	(338)	1,090	(932)	(1,005)	(1,992)	2,738	(1,057)	469
Derivative instrument	161	(515)	(17)	339	496	0	0	0	322	0	(193)	0	(32)	496	0
Other comprehensive income (loss)	5,770	(5,998)	1,955	(206)	1,119	(2,589)	(5,898)	1,132	1,749	(4,766)	(4,249)	(7,355)	1,521	(6,236)	7,610
Comprehensive income	$ (1,764)	1,182	8,101	9,780	9,216	8,688	6,773	10,576	17,881	17,349	19,063	26,037	$ 17,299	35,253	5,341
As Previously Reported
Net (loss) income		8,520	7,177	11,130	8,881	12,583	13,195	9,853	18,307	23,048	26,827	35,631		44,512	(1,705)
Other comprehensive (loss) income:
Foreign currency translation adjustments		(3,388)	233	104	(312)	(1,529)	(5,304)	1,470	337	(3,834)	(3,051)	(5,363)		(5,675)	7,141
Minimum pension liability, net of tax		(2,095)	1,739	(649)	935	(1,060)	(594)	(338)	1,090	(932)	(1,005)	(1,992)		(1,057)	469
Derivative instrument		(515)	(17)	339	496	0	0	0	322	0	(193)	0		496	0
Other comprehensive income (loss)		(5,998)	1,955	(206)	1,119	(2,589)	(5,898)	1,132	1,749	(4,766)	(4,249)	(7,355)		(6,236)	7,610
Comprehensive income		2,522	9,132	10,924	10,000	9,994	7,297	10,985	20,056	18,282	22,578	28,276		38,276	5,905
Restatement Adjustments
Net (loss) income		(1,340)	(1,031)	(1,144)	(784)	(1,306)	(524)	(409)	(2,175)	(933)	(3,515)	(2,239)		(3,023)	(564)
Other comprehensive (loss) income:
Foreign currency translation adjustments		0	0	0	0	0	0	0	0	0	0	0		0	0
Minimum pension liability, net of tax		0	0	0	0	0	0	0	0	0	0	0		0	0
Derivative instrument		0	0	0	0	0	0	0	0	0	0	0		0	0
Other comprehensive income (loss)		0	0	0	0	0	0	0	0	0	0	0		0	0
Comprehensive income		$ (1,340)	$ (1,031)	$ (1,144)	$ (784)	$ (1,306)	$ (524)	$ (409)	$ (2,175)	$ (933)	$ (3,515)	$ (2,239)		$ (3,023)	$ (564)