Consolidated Statements Of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Cash Flows from Operating Activities
Net income	$ 44,996	$ 29,844
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	9,294	8,939
Provision for uncollectible accounts receivable		4,249
Stock option expense	3,653	3,001
Benefit for deferred income taxes	(2,807)	(2,415)
Noncash long-term incentive compensation	1,721	827
Amortization of restricted stock awards	291	336
Amortization of debt issuance costs	128	129
Changes in operating assets and liabilities:
Decrease in accounts receivable	1,591	17,972
Decrease in inventories	60	322
Decrease in prepaid expenses	1,045	1,003
Decrease in accounts payable and other current liabilities	(7,911)	(10,766)
Increase in income taxes	13,642	14,655
Increase in other assets	(4,263)	(2,140)
Increase in other liabilities	3,758	1,992
Other sources/(uses)	(5)	838
Net cash provided by operating activities	65,193	68,786
Cash Flows from Investing Activities
Capital expenditures	(12,648)	(9,020)
Business combinations	(1,450)
Other sources/(uses)	181	(70)
Net cash used by investing activities	(13,917)	(9,090)
Cash Flows from Financing Activities
Proceeds from revolving line of credit	134,300	116,000
Payments on revolving line of credit	(90,500)	(76,000)
Purchases of treasury stock	(81,125)	(54,262)
Proceeds from exercise of stock options	8,923	5,635
Change in cash overdrafts payable	(6,671)	(8,607)
Capital stock surrendered to pay taxes on stock-based compensation	(6,377)	(4,744)
Dividends paid	(4,533)	(4,251)
Payments on other long-term debt	(2,500)	(1,875)
Other (uses)/sources	(228)	147
Net cash used by financing activities	(48,711)	(27,957)
Increase in Cash and Cash Equivalents	2,565	31,739
Cash and cash equivalents at beginning of year	11,121	15,310
Cash and cash equivalents at end of period	$ 13,686	$ 47,049