CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash flows from operating activities:
Net earnings	$ 313,903	$ 142,804	$ 227,970
Adjustments to reconcile net earnings to net cash provided by operations:
Depreciation and amortization	202,881	200,917	192,240
Provision (credit) for doubtful accounts	224	(467)	1,426
Provision (benefit) for deferred income taxes	(256,263)	51,296	62,755
Loss (gain) on disposition of assets	4,487	127	(1,672)
Equity in earnings of affiliates, net of distributions and contributions	732	(532)	449
Impairment of long-lived assets	105,712	0	0
Amortization of unearned share-based compensation	11,460	11,675	11,104
Amortization of major maintenance costs	21,207	19,869	22,126
Amortization of debt issuance costs	986	801	1,377
Increase (decrease) in cash flows resulting from changes in:
Accounts receivable	(60,405)	(12,750)	129,908
Inventory	19,673	3,182	(7,320)
Other assets	(17,049)	(30,853)	(15,551)
Income taxes payable	(11,823)	15,413	477
Accounts payable	20,758	(1,739)	(81,808)
Accrued and other liabilities	(3,105)	16,051	(19,201)
Net cash provided by operating activities	353,378	415,794	524,280
Cash flows from investing activities:
Capital expenditures	(177,222)	(231,066)	(345,475)
Acquisitions of businesses and marine equipment, net of cash acquired	(470,101)	(137,072)	(41,250)
Proceeds from disposition of assets	54,229	18,617	24,429
Net cash used in investing activities	(593,094)	(349,521)	(362,296)
Cash flows from financing activities:
Borrowings (payments) on bank credit facilities, net	268,616	(52,848)	160,784
Payments on long-term debt	(13,721)	0	(100,000)
Return of investment to noncontrolling interests	(862)	(1,976)	(1,778)
Proceeds from exercise of stock options	3,039	321	3,712
Purchase of treasury stock	0	(1,827)	(241,105)
Payments related to tax withholding for share-based compensation	(2,881)	(1,756)	(2,975)
Acquisitions of noncontrolling interest	(7)	(8,438)	0
Excess tax benefit from equity compensation plans	0	0	964
Net cash provided by (used in) financing activities	254,184	(66,524)	(180,398)
Increase (decrease) in cash and cash equivalents	14,468	(251)	(18,414)
Cash and cash equivalents, beginning of year	5,634	5,885	24,299
Cash and cash equivalents, end of year	20,102	5,634	5,885
Cash paid during the period:
Interest paid	21,663	19,878	20,586
Income taxes paid	27,196	18,162	69,584
Capital expenditures included in accounts payable	5,525	(2,037)	2,206
Non-cash investing activity:
Fair value of property transferred in acquisition	0	3,681	0
Stock issued in acquisition	366,554	0	0
Cash acquired in acquisition	98	0	0
Debt assumed in acquisition	$ 13,724	$ 0	$ 0