Condensed Consolidated Statements Of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Cash flows from operating activities:
Net income (loss)	$ 15,224	$ (22,818)
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation and amortization	55,659	56,377
Amortization of debt discount	2,659	2,303
Amortization of debt issuance costs	1,799	4,326
Share-based compensation	5,022	5,181
Deferred income taxes	(1,622)	(80)
Equity in losses of investment	271	304
Loss on disposition of assets, net	0	39
Loss on extinguishment of long-term debt	1,181	397
Unrealized gain on derivative contracts, net	(1,554)	(2,482)
Changes in operating assets and liabilities:
Accounts receivable, net	(14,319)	(10,122)
Other current assets	(9,662)	(10,957)
Income tax payable / receivable	(1,445)	(1,729)
Accounts payable and accrued liabilities	9,202	27,372
Other non-current, net	25,251	(32,510)
Net cash provided by operating activities	87,666	15,601
Cash flows from investing activities:
Capital expenditures	(41,969)	(94,396)
Proceeds from sale of assets	0	10,000
Net cash used in investing activities	(41,969)	(84,396)
Cash flows from financing activities:
Issuance of Convertible Senior Notes due 2023	125,000	0
Repurchase of Convertible Senior Notes due 2032	(60,362)	0
Proceeds from term loan	0	100,000
Repayment of term loan	(61,936)	(192,258)
Repayment of Nordea Q5000 Loan	(17,857)	(17,858)
Repayment of MARAD Debt	(3,226)	(3,073)
Debt issuance costs	(3,856)	(3,665)
Net proceeds from issuance of common stock	0	219,504
Payments related to tax withholding for share-based compensation	(1,058)	(1,306)
Proceeds from issuance of ESPP shares	332	279
Net cash provided by (used in) financing activities	(22,963)	101,623
Effect of exchange rate changes on cash and cash equivalents	(836)	960
Net increase in cash and cash equivalents	21,898	33,788
Cash and cash equivalents:
Balance, beginning of year	266,592	356,647
Balance, end of period	$ 288,490	$ 390,435