Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Cash flows from operating activities:
Net income	$ 18,626	$ 15,516
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	1,965	1,911
Bad debt provision	1,100	925
Deferred income tax	3,395	525
Stock-based compensation expense	1,118	884
Tax benefit from equity compensation plans	(509)	(499)
Amortization of premium on marketable securities	318	93
Unrealized loss (gain) on deferred compensation fund investments	278	(365)
Changes in operating assets and liabilities:
Accounts and notes receivable	(22,899)	(11,746)
Prepaid income taxes	(915)	912
Inventories and supplies	(1,619)	44
Prepaid expenses and other assets	(3,277)	(1,235)
Deferred compensation funding	(268)	451
Accounts payable and other accrued expenses	(4,100)	(2,351)
Accrued payroll, accrued and withheld payroll taxes	18,070	(21,002)
Accrued insurance claims	1,009	2,979
Deferred compensation liability	100	76
Income taxes payable	(2,703)	6,678
Net cash provided by (used in) operating activities	9,689	(6,204)
Cash flows from investing activities:
Disposals of fixed assets	114	41
Additions to property and equipment	(1,459)	(1,436)
Purchases of marketable securities	(4,966)	(989)
Sales of marketable securities	2,640	846
Net cash used in investing activities	(3,671)	(1,538)
Cash flows from financing activities:
Dividends paid	(13,158)	(12,655)
Reissuance of treasury stock pursuant to Dividend Reinvestment Plan	28	26
Tax benefit from equity compensation plans	509	499
Proceeds from the exercise of stock options	2,534	2,884
Net cash used in financing activities	(10,087)	(9,246)
Net change in cash and cash equivalents	(4,069)	(16,988)
Cash and cash equivalents at beginning of the period	33,189	75,280
Cash and cash equivalents at end of the period	29,120	58,292
Supplementary Cash Flow Information:
Cash paid for interest	155	22
Cash paid for income taxes, net of refunds	$ 11,201	$ 1,424