Consolidated Statements of Stockholders Equity - USD ($) $ in Thousands	Total	Common Stock Shares [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Treasury Stock [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]
Balance, Shares at Dec. 31, 2016		16,338,000
Balance at Dec. 31, 2016	$ 660,155		$ 1,633	$ 162,828	$ (14)	$ 516,980	$ (21,272)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of restricted stock and exercise of stock options, shares issued		676,000
Issuance of restricted stock and exercise of stock options, including excess income tax benefits	32,003		66	27,866	4,071
Treasury Stock, Shares		(27,000)
Purchase of treasury stock,treasury stock acquired in lieu of cash payment on stock option exercises and income tax withholding obligations	(4,057)			0	(4,057)
Business Acquisition, Equity Interest Issued or Issuable, Number of Shares		3,200,000
Issuance of common stock for acquisitions	413,139		320	412,819
Employee stock purchase plan, shares issued		23,000
Proceeds from employee stock purchase plan	2,705		2	2,703	0
Stock compensation	19,352			19,352
Other comprehensive income, net of tax	6,313						6,313
Net Income	68,644					68,644
Balance at Dec. 31, 2017	1,198,254		2,021	625,568	0	585,624	(14,959)
Balance, Shares at Dec. 31, 2017		20,210,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of restricted stock and exercise of stock options, shares issued		307,000
Issuance of restricted stock and exercise of stock options, including excess income tax benefits	14,275		28	8,090	6,157
Treasury Stock, Shares		(26,000)
Purchase of treasury stock,treasury stock acquired in lieu of cash payment on stock option exercises and income tax withholding obligations	(6,252)			0	(6,252)
Proceeds from employee stock purchase plan	0
Stock compensation	24,241			24,241
Other comprehensive income, net of tax	(1,986)						(1,986)
Net Income	28,793					28,793
Balance at Dec. 31, 2018	$ 1,263,655		2,049	657,899	(95)	620,747	(16,945)
Balance, Shares at Dec. 31, 2018	20,491,229	20,491,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative Effect of New Accounting Principle in Period of Adoption	$ 6,330
Issuance of restricted stock and exercise of stock options, shares issued		331,000
Issuance of restricted stock and exercise of stock options, including excess income tax benefits	7,732		25	(10,870)	18,577
Treasury Stock, Shares		(80,000)
Purchase of treasury stock,treasury stock acquired in lieu of cash payment on stock option exercises and income tax withholding obligations	(18,639)			0	(18,639)
Issuance of common stock for acquisitions	0
Proceeds from employee stock purchase plan	0
Stock compensation	21,918			21,918
Other comprehensive income, net of tax	1,543						1,543
Net Income	101,035					101,035
Balance at Dec. 31, 2019	$ 1,377,244		$ 2,074	$ 668,947	$ (157)	$ 721,782	$ (15,402)
Balance, Shares at Dec. 31, 2019	20,742,044	20,742,000