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Investment in unconsolidated subsidiary (Income Statement) (Details) - USD ($) $ in Thousands	2 Months Ended	3 Months Ended								12 Months Ended
	Feb. 22, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Schedule of Equity Method Investments [Line Items]
Net revenues		$ 147,203	$ 138,268	$ 142,723	$ 159,441	$ 196,148	$ 244,993	$ 284,415	$ 348,096	$ 587,635	$ 1,073,652	$ 1,739,717
Gross profit		30,613	29,284	5,281	34,557	2,906	65,762	84,883	109,126	99,735	262,677	559,452
Net income (loss)		(12,503)	(17,995)	(28,502)	(22,948)	(163,623)	6,718	8,865	28,656	(81,948)	(119,384)	174,377
The Company's earnings from equity investment		$ 617	$ 414	$ 216	$ 577	$ 2,543	$ 3,870	$ 3,840	$ 4,571	1,824	14,824	$ 25,164
Global Tubing LLC
Schedule of Equity Method Investments [Line Items]
Net revenues										71,473	103,532
Gross profit										16,899	45,333
Net income (loss)										3,795	30,888
The Company's earnings from equity investment										$ 1,824	$ 14,824
Subsequent Event \| Global Tubing LLC
Schedule of Equity Method Investments [Line Items]
Additional contribution to investment in subsidiary	$ 1,000