Consolidated Statements of Shareholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Retained Earnings	Treasury Stock
Balance at Dec. 31, 2013	$ 246,319	$ 481	$ 182,176	$ (46)	$ 202,210	$ (138,502)
Balance, shares at Dec. 31, 2013		48,148				(15,310)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	58,940				58,940
Issuance of shares pursuant to stock compensation plan	14,680		(17,449)			$ 32,129
Issuance of shares pursuant to stock compensation plan, shares						855
Stock compensation	14,819		14,819
Issuance of shares pursuant to employee stock purchase plan	$ 4,144		2,235			$ 1,909
Issuance of shares pursuant to employee stock purchase plan, shares	53					53
Federal income tax benefit related to exercise of stock options	$ 19,415		19,415
Treasury stock purchases	$ (22,817)					$ (22,817)
Treasury stock purchases, shares	(294)					(294)
Issuance of shares for acquisitions	$ 1,473		193			$ 1,280
Issuance of shares for acquisitions, shares	17					17
Balance at Dec. 31, 2014	$ 336,973	$ 481	201,389	(46)	261,150	$ (126,001)
Balance, shares at Dec. 31, 2014		48,148				(14,679)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	64,869				64,869
Issuance of shares pursuant to stock compensation plan	23,160		4,332			$ 18,828
Issuance of shares pursuant to stock compensation plan, shares						1,118
Stock compensation	20,182		20,182
Issuance of shares pursuant to employee stock purchase plan	$ 4,671		3,879			$ 792
Issuance of shares pursuant to employee stock purchase plan, shares	43					43
Federal income tax benefit related to exercise of stock options	$ 45,314		45,314
Treasury stock purchases	$ (645)					$ (645)
Treasury stock purchases, shares	(5)					(5)
Issuance of shares for acquisitions	$ 364,333		332,659			$ 31,674
Issuance of shares for acquisitions, shares	2,149					2,149
Balance at Dec. 31, 2015	$ 858,857	$ 481	607,755	(46)	326,019	$ (75,352)
Balance, shares at Dec. 31, 2015		48,148				(11,374)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	109,857				109,857
Issuance of shares pursuant to stock compensation plan	23,527		(82,273)			$ 105,800
Issuance of shares pursuant to stock compensation plan, shares						827
Stock compensation	29,747		29,747
Issuance of shares pursuant to employee stock purchase plan	6,236		1,434			$ 4,802
Issuance of shares pursuant to employee stock purchase plan, shares						47
Treasury stock purchases	(112,699)					$ (112,699)
Treasury stock purchases, shares						(882)
Issuance of shares for acquisitions	$ 0
Issuance of shares for acquisitions, shares	0
Balance at Dec. 31, 2016	$ 915,525	$ 481	$ 556,663	$ (46)	$ 435,876	$ (77,449)
Balance, shares at Dec. 31, 2016		48,148				(11,382)