Consolidated Statements Of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Cash flows from operating activities:
Net income	$ 77,396	$ 58,024	$ 21,850
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	7,496	7,660	7,269
Bad debt provision	4,629	4,335	4,470
Deferred income tax (benefit) expense	3,001	17,842	(15,059)
Stock-based compensation expense	4,252	3,541	3,080
Tax benefit from equity compensation plans	(2,981)	(1,873)	(2,626)
Amortization of premium on marketable securities	1,723	681	354
Unrealized (gain) loss on deferred compensation fund investments	(1,460)	24	(1,216)
Changes in operating assets and liabilities:
Accounts and notes receivable	(61,051)	(18,854)	(13,492)
Inventories and supplies	(1,492)	(846)	(3,015)
Prepaid expenses and other assets	(2,470)	(1,710)	(417)
Notes receivable — long term	(4,559)	0	600
Deferred compensation funding	2,732	(649)	(2,542)
Accounts payable and other accrued expenses	(4,251)	2,403	492
Accrued payroll, accrued and withheld payroll taxes	6,307	(28,314)	11,813
Accrued insurance claims	5,404	13,987	42,084
Deferred compensation liability	(731)	1,113	4,248
Income taxes payable	7,455	5,997	(163)
Net cash provided by operating activities	41,400	63,361	57,730
Cash flows from investing activities:
Disposals of fixed assets	275	267	83
Additions to property and equipment	(5,442)	(4,998)	(5,795)
Purchases of marketable securities	(29,449)	(75,150)	(5,140)
Sales of marketable securities	28,164	17,567	4,392
Net cash used in investing activities	(6,452)	(62,314)	(6,460)
Cash flows from financing activities:
Dividends paid	(53,342)	(51,375)	(49,077)
Reissuance of treasury stock pursuant to Dividend Reinvestment Plan	109	113	110
Tax benefit from equity compensation plans	2,981	1,873	2,626
Proceeds from the exercise of stock options	5,968	6,251	6,196
Net cash used in financing activities	(44,284)	(43,138)	(40,145)
Net change in cash and cash equivalents	(9,336)	(42,091)	11,125
Cash and cash equivalents at beginning of the period	33,189	75,280	64,155
Cash and cash equivalents at end of the period	23,853	33,189	75,280
Supplementary Cash Flow Information:
Cash paid for interest	574	258	156
Cash paid for income taxes, net of refunds	$ 32,532	$ 7,901	$ 25,080