Consolidated Statements Of Cash Flows (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Cash flows from operating activities:
Net income	$ 21,850	$ 47,129	$ 44,214
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	7,269	6,204	5,116
Bad debt provision	4,470	1,990	2,160
Deferred income tax benefits	(15,059)	(4,922)	(3,493)
Stock-based compensation expense	3,080	2,607	2,538
Amortization of premium on marketable securities	354	537	654
Unrealized loss on marketable securities	0	0	82
Unrealized gain on deferred compensation fund investments	(1,216)	(2,820)	(1,871)
Changes in operating assets and liabilities:
Accounts and notes receivable	(13,492)	(50,879)	(11,634)
Prepaid income taxes	0	0	405
Inventories and supplies	(3,015)	(3,772)	(3,531)
Notes receivable — long term	600	(3,956)	(340)
Deferred compensation funding	(2,542)	(4,369)	(4,051)
Accounts payable and other accrued expenses	492	25,961	13,664
Accrued payroll, accrued and withheld payroll taxes	11,813	6,349	6,142
Accrued insurance claims	42,084	3,616	4,908
Deferred compensation liability	4,248	7,721	6,337
Income taxes payable	(2,789)	(28)	1,906
Prepaid expenses and other assets	(417)	790	(2,830)
Net cash provided by operating activities	57,730	32,158	60,376
Cash flows from investing activities:
Disposals of fixed assets	83	158	26
Additions to property and equipment	(5,795)	(3,762)	(3,484)
Purchases of marketable securities	(5,140)	(6,598)	(10,833)
Sales of marketable securities	4,392	15,807	19,978
Cash paid for acquisition	0	(5,000)	0
Net cash (used in) provided by investing activities	(6,460)	605	5,687
Cash flows from financing activities:
Dividends paid	(49,077)	(46,707)	(44,093)
Reissuance of treasury stock pursuant to Dividend Reinvestment Plan	110	107	118
Tax benefit from equity compensation plans	2,626	2,615	2,649
Proceeds from the exercise of stock options	6,196	6,428	5,573
Net cash used in financing activities	(40,145)	(37,557)	(35,753)
Net change in cash and cash equivalents	11,125	(4,794)	30,310
Cash and cash equivalents at beginning of the period	64,155	68,949	38,639
Cash and cash equivalents at end of the period	75,280	64,155	68,949
Supplementary Cash Flow Information:
Cash paid for interest	156	4	3
Cash paid for income taxes, net of refunds	$ 25,080	$ 21,694	$ 24,681