Industry Segments and Geographic Information Industry Segments and Geographic Information 2 (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	$ 377,715	$ 561,241	$ 560,102
Transfers between geographic areas	(848)	(1,802)	(3,157)
Identifiable assets	1,132,839	1,271,922
Offshore Services [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Identifiable assets	710,006	822,699
UNITED STATES
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	225,835	411,284	390,403
Identifiable assets	285,765	338,054
Canada and Mexico [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	1,347	6,616	17,575
Identifiable assets	6,452	9,216
South America [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	11,583	13,188	16,067
Identifiable assets	10,388	13,632
Europe [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	90,303	93,327	91,997
Transfers between geographic areas	848	1,802	3,157
Identifiable assets	85,733	62,684
Africa [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	8,128	16,874	12,039
Identifiable assets	9,195	10,812
Asia and other [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	40,519	19,952	$ 32,021
Identifiable assets	$ 25,300	$ 14,825