Note 12 - Notes Payable (Details Textual) - USD ($) $ in Thousands			1 Months Ended		12 Months Ended
	Nov. 01, 2017	Aug. 10, 2017	Jan. 31, 2017	Nov. 30, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Aug. 09, 2017
Gain (Loss) on Extinguishment of Debt, Total					$ (12,762)	$ (1,753)	$ (45,674)
Notes Payable, Total					4,381,456	$ 4,596,140
Repayments of Medium-term Notes	$ 89,000	$ 211,000
Medium-term Notes, Total								$ 300,000
Debt Covenants Dividend Payment Restriction Maximum Payment					26,000
Long-term Line of Credit, Total					100,000
Senior Unsecured Note [Member]
Gain (Loss) on Extinguishment of Debt, Total					(12,800)
Notes Payable, Total					484,900
Medium-term Notes [Member]
Debt Instrument, Tender Offer, Partial Repayment Premium		$ 1,800
Unsecured Debt [Member]
Debt Issuance Costs, Net, Total					53,400
Term Loan [Member]
Unsecured Debt, Total					$ 650,000
Repayments of Long-term Debt, Total			$ 250,000	$ 400,000
London Interbank Offered Rate (LIBOR) [Member] | Term Loan [Member]
Debt Instrument, Basis Spread on Variable Rate					0.95%
Revolving Credit Facility [Member]
Debt Instrument, Interest Rate, Effective Percentage					3.31%	2.28%
Line of Credit Facility, Current Borrowing Capacity					$ 2,250,000
Line of Credit Facility Sub-limit					500,000
Revolving Credit Facility [Member] | Credit Facility Accordion Feature [Member]
Line of Credit Facility, Maximum Borrowing Capacity					$ 2,750,000
Revolving Credit Facility [Member] | London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument, Basis Spread on Variable Rate					0.875%
Letter of Credit [Member]
Long-term Line of Credit, Total					$ 300