Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015
Cash flows from operating activities:
Net income	$ 37,386	$ 31,804
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	3,912	3,831
Bad debt provision	2,150	1,675
Deferred income tax (benefit) expense	2,541	(1,466)
Stock-based compensation expense	2,091	1,733
Tax benefit from equity compensation plans, gross	(1,107)	(817)
Amortization of premium on marketable securities	663	185
Unrealized gain on deferred compensation fund investments	(82)	(482)
Changes in operating assets and liabilities:
Accounts and notes receivable	(43,190)	(6,879)
Inventories and supplies	(1,295)	69
Prepaid expenses and other assets	(4,787)	(2,199)
Deferred compensation funding	(971)	(243)
Accounts payable and other accrued expenses	552	(9,479)
Accrued payroll, accrued and withheld payroll taxes	9,329	(4,854)
Accrued insurance claims	4,448	6,354
Deferred compensation liability	1,473	952
Income taxes payable	7,098	13,329
Net cash provided by operating activities	20,211	33,513
Cash flows from investing activities:
Disposals of fixed assets	127	67
Additions to property and equipment	(2,954)	(2,289)
Purchases of marketable securities	(14,628)	(3,025)
Sales of marketable securities	6,284	2,813
Net cash used in investing activities	(11,171)	(2,434)
Cash flows from financing activities:
Dividends paid	(26,451)	(25,415)
Reissuance of treasury stock pursuant to Dividend Reinvestment Plan	57	54
Tax benefit from equity compensation plans, gross	1,107	817
Proceeds from the exercise of stock options	4,777	4,085
Net cash used in financing activities	(20,510)	(20,459)
Net change in cash and cash equivalents	(11,470)	10,620
Cash and cash equivalents at beginning of the period	33,189	75,280
Cash and cash equivalents at end of the period	21,719	85,900
Supplementary Cash Flow Information:
Cash paid for interest	254	35
Cash paid for income taxes, net of refunds	$ 12,262	$ 7,643