CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
OPERATING ACTIVITIES
NET INCOME	$ 44,854	$ 46,177	$ 15,811
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	89,040	81,870	84,215
Amortization of intangibles	4,002	4,352	4,174
Pension settlement expense	3,202	6,595	2,111
Share-based compensation expense	8,029	6,998	5,494
Provision for losses on accounts receivable	998	1,942	2,065
Deferred income tax provision (benefit)	16,435	4,692	(10,367)
Gain on sale of property and equipment	(2,225)	(1,461)	(153)
Changes in operating assets and liabilities:
Receivables	4,242	(26,892)	(24,200)
Prepaid expenses	362	(1,888)	(1,670)
Other assets	1,090	889	(1,015)
Income taxes	(8,918)	(11,972)	8,468
Accounts payable, accrued expenses, and other liabilities	(15,092)	32,464	8,571
NET CASH PROVIDED BY OPERATING ACTIVITIES	146,019	143,766	93,504
INVESTING ACTIVITIES
Purchases of property, plant and equipment, net of financings	(78,425)	(35,483)	(26,369)
Proceeds from sale of property and equipment	6,639	4,928	2,194
Purchases of short-term investments	(61,363)	(45,831)	(39,605)
Proceeds from sale of short-term investments	45,831	35,853	32,718
Business acquisitions, net of cash acquired	(29,813)	(2,647)	(4,146)
Capitalization of internally developed software	(8,512)	(8,418)	(7,668)
NET CASH USED IN INVESTING ACTIVITIES	(125,643)	(51,598)	(42,876)
FINANCING ACTIVITIES
Borrowings under credit facilities	70,000
Borrowings under accounts receivable securitization program	35,000
Payments on long-term debt	(100,813)	(40,440)	(43,176)
Net change in book overdrafts	3,843	2,486	(37)
Net change in restricted cash	2	516	7,756
Deferred financing costs	(875)	(76)	(71)
Payment of common stock dividends	(6,837)	(4,102)	(3,233)
Purchase of treasury stock	(12,765)
Proceeds from the exercise of stock options		1,136	2,785
NET CASH USED IN FINANCING ACTIVITIES	(12,445)	(40,480)	(35,976)
NET INCREASE IN CASH AND CASH EQUIVALENTS	7,931	51,688	14,652
Cash and cash equivalents at beginning of period	157,042	105,354	90,702
CASH AND CASH EQUIVALENTS AT END OF PERIOD	164,973	157,042	105,354
NONCASH INVESTING ACTIVITIES
Equipment financed	80,592	55,325	36
Accruals for equipment received	$ 748	$ 928	$ 324