Financial Instruments - Fair Value (Details) - Derivatives designated as cash flow hedges: - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Derivative assets:
Total derivative assets	$ 3,249	$ 3,928
Derivative liabilities:
Total derivative liabilities	34,466	11,376
Cash flow hedging
Derivative liabilities:
Total derivative liabilities	3,704	3,242
Cash flow hedging | Accrued liabilities | Interest rate caps
Derivative liabilities:
Total derivative liabilities	1,954	420
Cash flow hedging | Other long-term liabilities | Interest rate caps
Derivative liabilities:
Total derivative liabilities	1,750	2,822
Cash flow hedging | Other long-term liabilities | Cross currency swaps
Derivative liabilities:
Total derivative liabilities	30,762	8,134
Net investment hedging | Prepaid expenses and other current assets | Cross currency swaps
Derivative assets:
Total derivative assets	$ 3,249	$ 3,928