Condensed Consolidated Statements Of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Statement of Cash Flows [Abstract]
Net income	$ 49,763	$ 42,345
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	84,420	83,339
Amortization of debt discounts	4,642	4,238
Amortization of debt issuance costs	2,752	2,703
Share-based compensation	8,979	7,569
Deferred income taxes	2,347	(5,716)
Equity in losses of investment	82	378
Gain on disposition of assets, net	0	146
Loss on extinguishment of long-term debt	18	1,183
Unrealized gain on derivative contracts, net	(2,351)	(2,289)
Changes in operating assets and liabilities, net of acquisitions:
Accounts receivable, net	(45,399)	(15,769)
Other current assets	12,215	(5,662)
Income tax payable, net of income tax receivable	(3,143)	2,963
Accounts payable and accrued liabilities	(14,765)	6,968
Other, net	9,683	(28,723)
Net cash provided by operating activities	89,877	150,827
Cash flows from investing activities:
Capital expenditures	(45,636)	(55,431)
STL acquisition, net	(4,081)	0
Proceeds from sale of assets	2,550	25
Net cash used in investing activities	(47,167)	(55,406)
Cash flows from financing activities:
Issuance of Convertible Senior Notes due 2023	0	125,000
Repurchase of Convertible Senior Notes due 2032	0	(60,365)
Proceeds from term loan	35,000	0
Repayment of term loan	(34,567)	(62,872)
Repayment of Nordea Q5000 Loan	(26,786)	(26,786)
Repayment of MARAD Debt	(6,858)	(6,532)
Debt issuance costs	(1,544)	(3,867)
Payments related to tax withholding for share-based compensation	(1,345)	(1,058)
Proceeds from issuance of ESPP shares	462	506
Net cash used in financing activities	(35,638)	(35,974)
Effect of exchange rate changes on cash and cash equivalents	(191)	(947)
Net increase in cash and cash equivalents	6,881	58,500
Cash and cash equivalents:
Balance, beginning of year	279,459	266,592
Balance, end of period	$ 286,340	$ 325,092