Operating Leases - Narrative (Detail)	1 Months Ended	3 Months Ended		6 Months Ended
	Jun. 30, 2020 USD ($) ft² renewal_option	Jun. 30, 2020 USD ($) ft² renewal_option	Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($) ft² renewal_option	Jun. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)
Lessor, Lease, Description [Line Items]
Operating Lease Fixed And Variable Lease Payments		$ 77,100,000	$ 61,700,000	$ 152,200,000	$ 119,600,000
Operating Lease, Lease Income, Lease Payments		64,600,000	51,700,000	127,500,000	100,300,000
Operating Lease, Variable Lease Income		$ 12,500,000	$ 10,000,000.0	$ 24,700,000	19,300,000
Rentable Square Feet | ft²	1,197,073	1,197,073		1,197,073
Lessor, Operating Lease, Lessee Option To Purchase Underlying Asset, Purchase Price	$ 20,400,000	$ 20,400,000		$ 20,400,000
Right-of-use assets	4,400,000	4,400,000		4,400,000		$ 3,500,000
Lease liabilities	5,090,000	5,090,000		5,090,000		$ 3,800,000
Right of use asset obtained in exchange for operating lease liability upon implementation of ASC 842 on January 1, 2019				0	$ 3,262,000
Operating Lease, Liability, Payments, Leases Not Commenced	$ 1,900,000	$ 1,900,000		$ 1,900,000
Lessee, Operating Lease, Lease Not yet Commenced, Term of Contract	5 years	5 years		5 years
Ground Lease
Lessor, Lease, Description [Line Items]
Remaining lease term				3 years
Renewal term	10 years	10 years		10 years
Renewal options | renewal_option	2	2		2
Monthly rent expense				$ 9,000
Minimum | Office Leases
Lessor, Lease, Description [Line Items]
Remaining lease term				1 year
Renewal term	3 years	3 years		3 years
Maximum | Office Leases
Lessor, Lease, Description [Line Items]
Remaining lease term				5 years
Renewal term	5 years	5 years		5 years
2722 Fairview Street
Lessor, Lease, Description [Line Items]
Lessor, Operating Lease, Term of Contract	5 years	5 years		5 years
Lessor, Operating Lease, Rentable Square Feet | ft²	58,802
Rentable Square Feet | ft²	116,575	116,575		116,575