Note 10 - Stock-based Compensation (Tables)

3 Months Ended

Mar. 31, 2019

Notes Tables

Share-based Payment Arrangement, Cost by Plan [Table Text Block]

	Three Months Ended March 31,
	2019		2018
Cost of services-compensation	$	4,124	$	2,563
Selling, general and administrative		6,855		6,931
Total	$	10,979	$	9,494

Share-based Payment Arrangement, Option, Activity [Table Text Block]

	Number of Options			Weighted Average Exercise Price	Weighted Average- Remaining Contractual Terms		Aggregate- Intrinsic Value
Outstanding balance at December 31, 2018	4,402		$	17.07
Granted	560			39.52
Exercised	(1,443	)		16.03
Forfeitures	(134	)		18.99
Expired	-			-
Outstanding balance at March 31, 2019	3,385		$	21.19	6.85	$	33,767
Expected to vest at March 31, 2019	1,061		$	27.50	9.14	$	6,486
Exercisable at March 31, 2019	1,899		$	16.67	5.14	$	24,582

Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block]

	Three Months Ended March 31,
		2019		2018
Expected dividend yield		0	%	0	%
Risk-free interest rate		2.5	%	2.7	%
Expected volatility		40.9	%	42.5	%
Expected life (years)		6.4		6.0

Share-based Payment Arrangement, Restricted Stock Unit, Activity [Table Text Block]

	Number of Units			Weighted Average Grant Date Fair Value per Unit
Outstanding balance at December 31, 2018	1,488		$	17.60
Granted	408			34.43
Vesting of restricted stock units, net of units withheld for taxes	(377	)		16.88
Units withheld for taxes	(193	)		16.88
Forfeitures	(63	)		17.58
Outstanding balance at March 31, 2019	1,263		$	25.43