Industry Segments and Geographic Information Industry Segments and Geographic Information 2 (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	$ 1,037,933	$ 998,775	$ 723,098
Transfers between geographic areas	(1,802)	(3,157)	(2,025)
Identifiable assets	1,271,922	1,385,527	1,308,614
UNITED STATES
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	848,681	791,389	545,964
Transfers between geographic areas	0	0	0
Identifiable assets	1,099,048	1,211,759	1,131,650
Canada and Mexico [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	31,561	41,524	36,074
Transfers between geographic areas	0	0	0
Identifiable assets	53,015	59,355	62,537
South America [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	24,371	25,781	28,040
Transfers between geographic areas	0	0	0
Identifiable assets	30,111	25,122	23,352
Europe [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	94,533	93,262	80,721
Transfers between geographic areas	1,802	3,157	2,025
Identifiable assets	62,684	57,807	61,000
Africa [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	17,415	12,367	700
Transfers between geographic areas	0	0	0
Identifiable assets	10,812	14,772	3,696
Asia and other [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	21,372	34,452	31,599
Transfers between geographic areas	0	0	0
Identifiable assets	$ 16,252	$ 16,712	$ 26,379