Consolidated Statements of Cash Flows - USD ($) $ in Thousands		6 Months Ended
		Jun. 30, 2017	Jun. 30, 2016
Cash flows from operating activities:
Net income		$ 44,568	$ 37,386
Adjustments to reconcile net income to net cash (used in) provided by operating activities:
Depreciation and amortization		4,239	3,912
Bad debt provision		2,100	2,150
Deferred income tax expense		0	2,541
Stock-based compensation expense, net of tax benefit from equity compensation plans	[1]	315	984
Amortization of premium on marketable securities		569	663
Unrealized gain on deferred compensation fund investments		(2,304)	(82)
Changes in operating assets and liabilities:
Accounts and notes receivable		(69,187)	(43,190)
Inventories and supplies		(238)	(1,295)
Prepaid expenses and other assets		(6,089)	(4,787)
Deferred compensation funding		98	(971)
Accounts payable and other accrued expenses		5,550	552
Accrued payroll, accrued and withheld payroll taxes		1,572	9,329
Income taxes payable	[1]	7,343	7,098
Accrued insurance claims		2,399	4,448
Deferred compensation liability		2,504	1,473
Net cash (used in) provided by operating activities		(6,561)	20,211
Cash flows from investing activities:
Disposals of fixed assets		169	127
Additions to property and equipment		(2,674)	(2,954)
Purchases of marketable securities		(15,939)	(14,628)
Sales of marketable securities		14,681	6,284
Cash paid for acquisition		(2,584)	0
Net cash used in investing activities		(6,347)	(11,171)
Cash flows from financing activities:
Dividends paid		(27,374)	(26,451)
Reissuance of treasury stock pursuant to Dividend Reinvestment Plan		48	57
Tax benefit from equity compensation plans	[1]	0	1,107
Proceeds from the exercise of stock options		7,257	4,777
Net proceeds from short-term borrowings		16,182	0
Net cash used in financing activities		(3,887)	(20,510)
Net change in cash and cash equivalents		(16,795)	(11,470)
Cash and cash equivalents at beginning of the period		23,853	33,189
Cash and cash equivalents at end of the period		$ 7,058	$ 21,719

[1] The Company adopted the provisions of ASU 2016-09 prospectively, and as such the amounts reflected for the six months ended June 30, 2016 have not been adjusted.