Note 10 - Stock-based Compensation (Tables)

12 Months Ended

Dec. 31, 2016

Notes Tables

Schedule of Share-based Compensation, Employee Stock Purchase Plan, Activity [Table Text Block]

Year Ended December 31,	2016
Shares purchased pursuant to 2009 ESPP		94,909
Weighted average per share price of shares purchased	$	73.67
Weighted average per share discount from market value for shares purchased	$	13.00

As of December 31,	2016
Shares available for purchase pursuant to 2009 ESPP		372,751

Schedule of Share-based Compensation, Restricted Stock and Restricted Stock Units Activity [Table Text Block]

	RSUs			Weighted average grant date fair value
Balance, December 31, 2015		411,074		$	59.13
Granted		144,152			82.90
Vested		(240,433	)		47.45
Forfeited		(15,809	)		79.34
Balance, December 31, 2016		298,984			80.37

Disclosure of Share-based Compensation Arrangements by Share-based Payment Award [Table Text Block]

Year Ended December 31,	2016		2015		2014
Per share intrinsic value of non-vested stock granted	$	82.90	$	88.74	$	68.99
Weighted average per share discount for compensation expense recognized under the 2009 ESPP		13.00		15.89		11.92
Total intrinsic value of stock options exercised (in millions)		—		0.5		3.1
Fair value of non-vested stock that vested during the period (in millions)		47.5		19.3		18.9
Stock-based compensation recognized in Consolidated Statements of Operations, as a component of selling, general and administrative expense (in millions)		11.0		11.9		7.4
Tax benefit recognized in Consolidated Statements of Operations (in millions)		3.8		4.2		2.6
Cash received from options exercised and shares purchased under all share-based arrangements (in millions)		7.0		6.5		4.9
Tax deduction realized related to stock options exercised (in millions)		8.9		7.6		8.4