Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Purchase of common stock	$ (63,570)	$ 10,345	$ 0
Withholding taxes paid for conversion of employee stock awards	2,300	1,310	940
OPERATING ACTIVITIES:
Net earnings from continuing operations	21,060	39,155	32,074
Net earnings (loss) from discontinued operations	2,428	2,067	(2,214)
Adjustments to reconcile net earnings to net cash provided by operating activities:
Depreciation and amortization	140,002	125,443	108,254
Pension and post-retirement	11,532	6,920	8,492
Deferred income taxes	13,807	23,691	17,757
Amortization of stock-based compensation	3,165	2,454	2,924
Amortization of DHL promissory note	0	(1,550)	(6,200)
Net (gain) loss on financial instruments	(969)	(920)	(1,096)
Changes in assets and liabilities:
Accounts receivable	(9,597)	(14,410)	9,582
Inventory and prepaid supplies	(5,269)	(3,896)	(4,164)
Accounts payable	5,603	4,424	(803)
Unearned revenue	(3,216)	(1,116)	1,148
Accrued expenses, salaries, wages, benefits and other liabilities	5,678	8,375	344
Pension and post-retirement assets	(11,819)	(16,098)	(14,662)
Other	1,611	470	(1,711)
NET CASH PROVIDED BY OPERATING ACTIVITIES	193,092	175,009	149,725
INVESTING ACTIVITIES:
Capital expenditures	(264,477)	(158,714)	(112,184)
Proceeds from property and equipment	12,380	6,841	3,602
Investment in nonconsolidated affiliate	(17,395)	0	(15,000)
NET CASH (USED IN) INVESTING ACTIVITIES	(269,492)	(151,873)	(123,582)
FINANCING ACTIVITIES:
Principal payments on long term obligations	(44,069)	(69,344)	(79,221)
Proceeds from borrowings	185,000	45,000	45,000
Funding for hangar construction	0	0	7,879
NET CASH PROVIDED BY (USED IN) FINANCING ACTIVITIES	75,061	(35,999)	(27,282)
NET (DECREASE) IN CASH AND CASH EQUIVALENTS	(1,339)	(12,863)	(1,139)
CASH AND CASH EQUIVALENTS AT BEGINNING OF YEAR	17,697	30,560	31,699
CASH AND CASH EQUIVALENTS AT END OF PERIOD	16,358	17,697	30,560
SUPPLEMENTAL CASH FLOW INFORMATION:
Interest paid, net of amount capitalized	10,738	10,748	13,576
Federal alternative minimum and state income taxes paid	923	870	604
SUPPLEMENTAL NON-CASH INFORMATION:
Debt extinguished	0	1,550	6,200
Accrued capital expenditures	9,118	7,033	7,648
Net (gain) loss on financial instruments	$ (18,107)	$ 920	$ 1,096