Note 14 - Quarterly Results of Operations (Unaudited) - Quarterly Results of Operations (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended										12 Months Ended
	Dec. 31, 2019	[1]	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	[1]	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenue	$ 233,135		$ 222,914	$ 219,298	$ 219,181	$ 272,268		$ 243,303	$ 196,318	$ 173,566	$ 894,528	$ 885,455	$ 705,007
Operating income (loss)	3,695		(1,931)	8,844	5,426	22,315		16,181	14,065	6,425	16,034	58,986	28,155
Net income	$ 1,162		$ (3,189)	$ 6,071	$ 4,433	$ 16,501		$ 11,614	$ 9,971	$ 4,417	$ 8,477	$ 42,503	$ 55,439
Basic income (loss) per share (in dollars per share)	$ 0.06		$ (0.17)	$ 0.33	$ 0.24	$ 0.91		$ 0.63	$ 0.54	$ 0.24	$ 0.46	$ 2.32	$ 3.03
Diluted income (loss) per share (in dollars per share)	$ 0.05		$ (0.17)	$ 0.33	$ 0.24	$ 0.89		$ 0.63	$ 0.54	$ 0.24	$ 0.45	$ 2.30	$ 3.02

[1] Includes $40.1 million one-time benefit related to the Tax Act.