Note 19 - Selected Quarterly Financial Data (Unaudited) - Quarterly Financial Data (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended									12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	[1]	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Revenue	$ 289,559	$ 306,520	$ 305,419	$ 283,599		$ 280,805	$ 288,951	$ 288,949	$ 273,527	$ 1,185,097	$ 1,132,232	$ 1,050,134
Operating income	21,965	23,776	19,358	17,694		19,038	21,497	18,734	15,962	82,793	75,231	69,362
Net income	$ 12,673	$ 13,437	$ 10,583	$ 9,891		$ 10,750	$ 11,545	$ 9,174	$ 7,900	$ 46,584	$ 39,369	$ 40,030
Earnings per Share:
Basic (in dollars per share)	$ 0.67	$ 0.71	$ 0.56	$ 0.52		$ 0.56	$ 0.60	$ 0.47	$ 0.41	$ 2.45	$ 2.04	$ 2.04
Diluted (in dollars per share)	$ 0.65	$ 0.70	$ 0.55	$ 0.51		$ 0.55	$ 0.59	$ 0.47	$ 0.40	$ 2.40	$ 2	$ 2
Weighted-average common shares outstanding (in thousands)
Basic (in shares)	18,988	18,965	19,008	18,994		19,102	19,316	19,475	19,450	18,989	19,335	19,608
Diluted (in shares)	19,512	19,329	19,293	19,273		19,373	19,556	19,706	19,838	19,416	19,663	19,997

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