Debt Obligations - Additional Information (Details)		6 Months Ended
	Aug. 22, 2017 USD ($) Tranche	Sep. 30, 2017 GBP (£)	Nov. 01, 2017 USD ($)	Oct. 20, 2017 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2017 HKD	Jul. 25, 2017 GBP (£)	Apr. 01, 2017 USD ($)	Apr. 01, 2017 HKD	Dec. 31, 2016 USD ($)	Dec. 31, 2016 HKD
Term Loan Facility
Line of Credit Facility [Line Items]
Bridge loan | £		£ 344,200,000					£ 1,115,000,000.000
Senior Unsecured Revolving Credit Facility | 2017 Credit Facility | Federal funds effective rate
Line of Credit Facility [Line Items]
Interest rate margin	0.50%
Senior Unsecured Revolving Credit Facility | 2017 Credit Facility | FRBNY rate
Line of Credit Facility [Line Items]
Interest rate margin	0.50%
Senior Unsecured Revolving Credit Facility | 2017 Credit Facility | One-Month LIBOR
Line of Credit Facility [Line Items]
Interest rate margin	1.00%
Senior Unsecured Revolving Credit Facility | 2017 Credit Facility | Canadian Prime Rate
Line of Credit Facility [Line Items]
Interest rate margin	1.00%
Senior Unsecured Revolving Credit Facility | 2017 Credit Facility | One-month CDOR
Line of Credit Facility [Line Items]
Interest rate margin	0.10%
Senior Unsecured Revolving Credit Facility | HK Credit Facility | Line of credit
Line of Credit Facility [Line Items]
Maximum borrowing capacity (up to)										$ 12,800,000	HKD 100,000,000.0
Line of credit, current obligations					$ 0			$ 5,800,000	HKD 45,000,000
Amount available for future borrowings					11,300,000	HKD 88,200,000
Minimum commitment, amount | HKD											5,000,000
Senior Unsecured Revolving Credit Facility | HK Credit Facility | HIBOR | Line of credit
Line of Credit Facility [Line Items]
Interest rate margin		1.50%
Senior Unsecured Revolving Credit Facility | HK Credit Facility, Bank Guarantees | Line of credit
Line of Credit Facility [Line Items]
Bank guarantees supported by facility					1,500,000	HKD 11,800,000
Stand-by Letters of Credit | 2017 Credit Facility
Line of Credit Facility [Line Items]
Letter of credit outstanding					11,300,000
Business Card Facility | HK Credit Facility | Line of credit
Line of Credit Facility [Line Items]
Maximum borrowing capacity (up to)										$ 100,000	HKD 400,000.0
Line of credit | Senior Unsecured Revolving Credit Facility | 2017 Credit Facility
Line of Credit Facility [Line Items]
Initiation date	Aug. 22, 2017
Maximum borrowing capacity (up to)	$ 1,000,000,000
Expiration date	Aug. 22, 2022
Adjusted leverage ratio (no greater than)	3.5
Line of credit, current obligations					0
Amount available for future borrowings					$ 988,700,000
Line of credit | Senior Unsecured Revolving Credit Facility | 2017 Credit Facility | Minimum
Line of Credit Facility [Line Items]
Commitment fee percentage	0.10%
Line of credit | Senior Unsecured Revolving Credit Facility | 2017 Credit Facility | Maximum
Line of Credit Facility [Line Items]
Commitment fee percentage	0.25%
Line of credit | Senior Unsecured Revolving Credit Facility | 2015 Credit Facility
Line of Credit Facility [Line Items]
Line of credit, current obligations								$ 127,300,000.0
Line of credit | Letter of Credit | 2017 Credit Facility
Line of Credit Facility [Line Items]
Maximum borrowing capacity (up to)	$ 75,000,000
Line of credit | Bridge loan | 2017 Credit Facility
Line of Credit Facility [Line Items]
Maximum borrowing capacity (up to)	50,000,000
Unsecured debt | Term Loan Facility
Line of Credit Facility [Line Items]
Maximum borrowing capacity (up to)	$ 1,000,000,000
Number of loan tranches | Tranche	2
Additional maximum borrowing capacity	$ 500,000,000.0
Periodic payment percentage	2.50%
Unsecured debt | Term Loan Facility | Third anniversary of initial borrowing
Line of Credit Facility [Line Items]
Maximum borrowing capacity (up to)	$ 600,000,000.0
Unsecured debt | Term Loan Facility | Fifth anniversary of initial borrowing
Line of Credit Facility [Line Items]
Maximum borrowing capacity (up to)	$ 400,000,000.0
Unsecured debt | Term Loan Facility | Minimum
Line of Credit Facility [Line Items]
Commitment fee percentage	0.10%
Unsecured debt | Term Loan Facility | Maximum
Line of Credit Facility [Line Items]
Commitment fee percentage	0.25%
Subsequent event | Term Loan Facility
Line of Credit Facility [Line Items]
Bridge loan				$ 0
Subsequent event | Senior notes | 4.00% Senior Notes
Line of Credit Facility [Line Items]
Aggregate principal amount				$ 450,000,000.0
Stated interest rate percentage				4.00%
Subsequent event | Unsecured debt | Term Loan Facility
Line of Credit Facility [Line Items]
Long-term Line of Credit			$ 1,000,000,000