Condensed Consolidated Statements Of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Statement of Cash Flows [Abstract]
Net income	$ 18,141	$ 15,224
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	56,512	55,659
Amortization of debt discounts	3,070	2,659
Amortization of debt issuance costs	1,896	1,799
Share-based compensation	6,501	5,022
Deferred income taxes	845	(1,622)
Equity in losses of investment	69	271
Loss on extinguishment of long-term debt	18	1,181
Unrealized gain on derivative contracts, net	(1,740)	(1,554)
Changes in operating assets and liabilities, net of acquisitions:
Accounts receivable, net	(30,656)	(14,319)
Other current assets	(2,957)	(9,662)
Income tax payable	(3,122)	(1,445)
Accounts payable and accrued liabilities	97	9,202
Other, net	16,113	(25,251)
Net cash provided by operating activities	32,561	87,666
Cash flows from investing activities:
Capital expenditures	(27,458)	(41,969)
STL acquisition, net	(4,081)	0
Proceeds from sale of assets	2,525	0
Net cash used in investing activities	(29,014)	(41,969)
Cash flows from financing activities:
Issuance of Convertible Senior Notes due 2023	0	125,000
Repurchase of Convertible Senior Notes due 2032	0	(60,362)
Proceeds from term loan	35,000	0
Repayment of term loan	(33,692)	(61,936)
Repayment of Nordea Q5000 Loan	(17,857)	(17,857)
Repayment of MARAD Debt	(3,387)	(3,226)
Debt issuance costs	(1,485)	(3,856)
Payments related to tax withholding for share-based compensation	(1,329)	(1,058)
Proceeds from issuance of ESPP shares	281	332
Net cash used in financing activities	(22,469)	(22,963)
Effect of exchange rate changes on cash and cash equivalents	605	(836)
Net increase (decrease) in cash and cash equivalents	(18,317)	21,898
Cash and cash equivalents:
Balance, beginning of year	279,459	266,592
Balance, end of period	$ 261,142	$ 288,490