Financial Instruments and Fair Value Measurements - Narrative (Details) $ in Thousands, £ in Millions	1 Months Ended		3 Months Ended		9 Months Ended
	Jul. 31, 2020 USD ($) derivative	Jun. 30, 2020 USD ($) derivative	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2020 GBP (£) hybrid_instrument derivative	Sep. 30, 2020 USD ($) hybrid_instrument derivative	Feb. 29, 2020 USD ($) derivative	Dec. 31, 2019 USD ($)	May 31, 2019 GBP (£) derivative	May 31, 2019 USD ($) derivative
Derivative [Line Items]
Aggregate notional amount								$ 1,223,300		$ 673,400
Number of hybrid debt instruments | hybrid_instrument							2	2
Interest expense
Derivative [Line Items]
Unrealized gains (losses) reclassified to income statement			$ 3,000		$ 8,300
Currency exchange swap | Not designated as hedging instrument
Derivative [Line Items]
Aggregate notional amount							£ 224.9	$ 300,100		$ 0
Treasury rate locks | Cash flow hedge
Derivative [Line Items]
Aggregate notional amount									$ 500,000
Number of derivative instruments | derivative									5
Number of instruments terminated | derivative		5
Forward-starting swap | Cash flow hedge
Derivative [Line Items]
Aggregate notional amount		$ 500,000
Number of derivative instruments | derivative		6					6	6
Number of derivatives | derivative							4	4
Redesignated forward starting swaps
Derivative [Line Items]
Aggregate notional amount	$ 350,000
Number of instruments being amortized and not terminated | derivative	4
Cross-currency swaps | Cash flow hedge
Derivative [Line Items]
Aggregate notional amount											£ 130.0	$ 166,000
Number of derivative instruments | derivative											4	4
Cross-currency swaps | Foreign exchange gains
Derivative [Line Items]
Unrealized gains (losses) reclassified to income statement			$ 6,300	$ (5,700)	$ (5,900)	$ (7,100)
Cross-currency swap unrealized gains expected to be reclassified within next twelve months								$ 1,700
Interest rate swaps | Interest expense
Derivative [Line Items]
Unrealized gains (losses) reclassified to income statement				$ 890		$ 2,000
Interest rate swaps and treasury locks | Interest expense
Derivative [Line Items]
Interest rate swap unrealized loss expected to be reclassified within next twelve months								$ 12,100