Business Combination (Schedule of Assets and Liabilities) (Details) $ in Thousands	3 Months Ended
	Dec. 31, 2018 USD ($) ship	Jul. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Assets
Goodwill	$ 1,378,353		$ 288,512	$ 288,386
Liabilities
Cash held as collateral		$ 32,000
Number of ships under capital leases | ship	2
Intangible assets	$ 494,560
Silversea Cruises
Assets
Cash and cash equivalents	103,865	103,865
Cash and cash equivalents, measurement period adjustments	0
Trade and other receivables, net	7,163	5,640
Trade and other receivables, net, measurement period adjustments	1,523
Inventories	18,331	19,004
Inventories, measurement period adjustments	(673)
Prepaid expenses and other assets	120,496	119,920
Prepaid expenses and other assets, measurement period adjustments	576
Derivative financial instruments	2,886	2,886
Derivative financial instruments, measurement period adjustments	0
Property and equipment, net	1,114,270	1,109,467
Property and equipment, net, measurement period adjustments	4,803
Goodwill	1,090,010	1,086,539
Goodwill, measurement period adjustments	3,471
Other assets	498,457	494,657
Other assets, measurement period adjustments	3,800
Total assets acquired	2,955,478	2,941,978
Total assets acquired, measurement period adjustments	13,500
Liabilities
Current portion of long-term debt	26,851	26,851
Current portion of long-term debt, measurement period adjustments	0
Accounts payable	36,960	36,960
Accounts payable, measurement period adjustments	0
Customer deposits	453,798	453,798
Customer deposits, measurement period adjustments	0
Long-term debt	727,935	727,935
Long-term debt, measurement period adjustments	0
Other long-term liabilities	23,860	12,320
Other long-term liabilities, measurement period adjustments	11,540
Total liabilities assumed	1,353,708	1,340,208
Total liabilities assumed, measurement period adjustments	13,500
Redeemable noncontrolling interest	537,770	537,770
Redeemable noncontrolling interest, measurement period adjustments	0
Total purchase price	1,064,000	1,064,000
Total purchase price, measurement period adjustments	$ 0
Number of ships under capital leases | ship	2
Capital leases assets		156,000
Accrued interest | Silversea Cruises
Liabilities
Current liabilities, other	$ 1,773	1,773
Current liabilities, other, measurement period adjustments	0
Accrued expenses and other liabilities | Silversea Cruises
Liabilities
Current liabilities, other	82,531	$ 80,571
Current liabilities, other, measurement period adjustments	$ 1,960