CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
OPERATING ACTIVITIES
Net income	$ 18,652	$ 44,854	$ 46,177
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	98,814	89,040	81,870
Amortization of intangibles	4,239	4,002	4,352
Impairment of long-lived assets	6,244
Pension settlement expense	3,229	3,202	6,595
Share-based compensation expense	7,588	8,029	6,998
Provision for losses on accounts receivable	1,643	998	1,942
Deferred income tax provision	9,522	16,435	4,692
Gain on sale of property and equipment	(3,335)	(2,225)	(1,461)
Changes in operating assets and liabilities:
Receivables	(25,570)	4,242	(26,892)
Prepaid expenses	(1,393)	362	(1,888)
Other assets	(4,355)	1,090	889
Income taxes	6,236	(8,918)	(11,972)
Accounts payable, accrued expenses, and other liabilities	(11,256)	(15,092)	32,464
NET CASH PROVIDED BY OPERATING ACTIVITIES	110,258	146,019	143,766
INVESTING ACTIVITIES
Purchases of property, plant and equipment, net of financings	(68,271)	(78,425)	(35,483)
Proceeds from sale of property and equipment	8,804	6,639	4,928
Purchases of short-term investments	(69,400)	(61,363)	(45,831)
Proceeds from sale of short-term investments	74,167	45,831	35,853
Business acquisitions, net of cash acquired	(24,780)	(29,813)	(2,647)
Proceeds from sale of subsidiaries	2,780
Capitalization of internally developed software	(10,472)	(8,512)	(8,418)
NET CASH USED IN INVESTING ACTIVITIES	(87,172)	(125,643)	(51,598)
FINANCING ACTIVITIES
Borrowings under credit facilities		70,000
Borrowings under accounts receivable securitization program		35,000
Payments on long-term debt	(52,202)	(100,813)	(40,440)
Net change in book overdrafts	(4,171)	3,843	2,486
Net change in restricted cash	422	2	516
Deferred financing costs		(875)	(76)
Payment of common stock dividends	(8,318)	(6,837)	(4,102)
Purchases of treasury stock	(9,510)	(12,765)
Proceeds from the exercise of stock options			1,136
NET CASH USED IN FINANCING ACTIVITIES	(73,779)	(12,445)	(40,480)
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	(50,693)	7,931	51,688
Cash and cash equivalents at beginning of period	164,973	157,042	105,354
CASH AND CASH EQUIVALENTS AT END OF PERIOD	114,280	164,973	157,042
NONCASH INVESTING ACTIVITIES
Equipment financed	83,366	80,592	55,325
Accruals for equipment received	$ 397	$ 748	$ 928