Note 6 - Segment Reporting - Segment Information (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Total adjusted EBITDA		$ 424,552	$ 317,300	$ 276,522
Interest expense		(40,956)	(42,667)	(44,568)
Depreciation and amortization		(47,408)	(51,988)	(54,418)
Non-cash write-down and other adjustments (1)	[1]	(3,532)	(2,923)	(357)
Non-cash share-based compensation expense (2)	[2]	(14,563)	(10,205)	(9,493)
Gain (Loss) on Extinguishment of Debt, Total	[3]	(1,332)		(574)
Gain Loss on Change in Cash Flows Related to Debt	[4]			(2,957)
Transaction costs and credit facility fees (5)	[5]	(3,883)	(2,145)	(2,442)
Business optimization expenses (6)	[6]	(952)	(2,912)	(7,316)
Other		(850)	(761)	(700)
Income before provision for income taxes		311,076	203,699	153,697
Assets		2,426,314	2,025,965	1,865,969
Depreciation and Amortization		47,408	51,988	54,418
Capital expenditures		47,601	33,261	30,467
Domestic [Member]
Total adjusted EBITDA		388,685	290,290	259,563
Depreciation and amortization		(35,586)	(37,962)	(42,346)
Assets		1,868,554	1,612,607	1,525,950
Depreciation and Amortization		35,586	37,962	42,346
Capital expenditures		38,242	29,258	26,936
International [Member]
Total adjusted EBITDA		35,867	27,010	16,959
Depreciation and amortization		(11,822)	(14,026)	(12,072)
Assets		557,760	413,358	340,019
Depreciation and Amortization		11,822	14,026	12,072
Capital expenditures		$ 9,359	$ 4,003	$ 3,531

[1] Includes gains/losses on disposal of assets, unrealized mark-to-market adjustments on commodity contracts, and certain foreign currency and purchase accounting related adjustments.

[2] Represents share-based compensation expense to account for stock options, restricted stock and other stock awards over their respective vesting periods.

[3] Represents the write-off of original issue discount and capitalized debt issuance costs due to voluntary debt prepayments.

[4] For the year ended December 31, 2016, represents a non-cash loss relating to the continued 25 basis point increase in borrowing costs as a result of the credit agreement leverage ratio remaining above 3.0 times based on projections at that time. Following the May 2017 Term Loan amendment, which removed the pricing grid based on leverage ratio achieved, gains or losses on changes in contractual interest rate will no longer be recorded in the statements of comprehensive income. Refer to Note 10, "Credit Agreements," to the consolidated financial statements for further information on the gains and losses on changes in the contractual interest rate.

[5] Represents transaction costs incurred directly in connection with any investment, as defined in our credit agreement, equity issuance, debt issuance or refinancing, together with certain fees relating to our senior secured credit facilities.

[6] Represents charges relating to business optimization and restructuring costs.