Consolidated Statements Of Cash Flows (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Cash flows from operating activities:
Net income	$ 14,639	$ 14,954
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Depreciation and amortization	1,757	1,352
Bad debt provision	750	450
Deferred income benefits	3,075	305
Stock-based compensation expense	762	583
Amortization of premium on marketable securities	88	154
Unrealized gain on deferred compensation fund investments	(264)	(789)
Changes in operating assets and liabilities:
Accounts and notes receivable	(6,855)	(10,695)
Prepaid income taxes	(1,007)	(1,628)
Inventories and supplies	(309)	79
Prepaid expenses and other assets	(2,106)	(1,182)
Deferred compensation funding	(798)	(1,423)
Accounts payable and other accrued expenses	(469)	7,670
Accrued payroll, accrued and withheld payroll taxes	9,679	(15,282)
Accrued insurance claims	26	19
Deferred compensation liability	1,230	2,312
Income taxes payable	(1,878)	(1,906)
Net cash provided by (used in) operating activities	18,320	(5,027)
Cash flows from investing activities:
Disposals of fixed assets	60	164
Additions to property and equipment	(1,513)	(968)
Purchases of marketable securities	(1,228)	(1,537)
Sales of marketable securities	939	185
Net cash used in investing activities	(1,742)	(2,156)
Cash flows from financing activities:
Dividends paid	(12,077)	(11,415)
Reissuance of treasury stock pursuant to Dividend Reinvestment Plan	0	27
Tax benefit from equity compensation plans	477	709
Proceeds from the exercise of stock options	2,559	3,640
Net cash used in financing activities	(9,041)	(7,039)
Net change in cash and cash equivalents	7,537	(14,222)
Cash and cash equivalents at beginning of the period	64,155	68,949
Cash and cash equivalents at end of the period	71,692	54,727
Supplementary Cash Flow Information:
Cash paid for interest	13	0
Cash paid for income taxes, net of refunds	7,821	6,523
Issuance of Common Stock in 2014 and 2013, respectively, pursuant to Employee Stock Purchase Plan	$ 1,851	$ 1,842