Note 2 - Summary of Significant Accounting Policies (Details Textual) - USD ($) $ in Thousands	3 Months Ended									9 Months Ended	12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016		Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Sep. 30, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Number of Reporting Units											1
Goodwill, Impaired, Accumulated Impairment Loss		$ 0								$ 0
Goodwill, Impairment Loss										$ 0
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax							$ 4,000
Other Comprehensive Income (Loss), Tax											$ 2,200	$ 1,000	$ 400
Revenues	$ 289,559	$ 306,520	$ 305,419	$ 283,599	[1]	$ 280,805	$ 288,951	$ 288,949	$ 273,527		1,185,097	1,132,232	1,050,134
Foreign Financial Institutions, Actual Deposits	$ 5,400					$ 6,700					5,400	6,700
Income Tax Expense (Benefit)											27,923	24,231	24,120
Net Cash Provided by (Used in) Operating Activities, Continuing Operations											79,563	76,319	79,160
Reclassification of Deferred Tax Assets and Liabilities to Noncurrent Classification [Member] | December 31, 2015 [Member]
Prior Period Reclassification Adjustment				$ 8,000
Accounting Standards Update 2016-09 [Member] | New Accounting Pronouncement, Early Adoption, Effect [Member]
Income Tax Expense (Benefit)											(700)
Net Cash Provided by (Used in) Operating Activities, Continuing Operations											700
Federal Government Agencies And Departments [Member]
Revenues											$ 563,000	$ 540,000	$ 532,000
Federal Government Agencies And Departments [Member] | Customer Concentration Risk [Member] | Sales Revenue, Net [Member]
Concentration Risk, Percentage											48.00%	48.00%	51.00%
International Clients [Member] | Geographic Concentration Risk [Member] | Sales Revenue, Net [Member]
Concentration Risk, Percentage											10.00%	11.00%	12.00%
Minimum [Member]
Property, Plant and Equipment, Useful Life											2 years
Finite-Lived Intangible Asset, Useful Life											4 years
Minimum [Member] | Other Assets [Member]
Finite-Lived Intangible Asset, Useful Life											3 years
Maximum [Member]
Property, Plant and Equipment, Useful Life											7 years
Finite-Lived Intangible Asset, Useful Life											10 years
Maximum [Member] | Other Assets [Member]
Finite-Lived Intangible Asset, Useful Life											5 years

[1] Includes adjustments for the adoption ASU 2016-09 in the second quarter of 2016.