Summary of Significant Accounting Policies - Narrative (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Jan. 01, 2019
Accounting Policies [Line Items]
Operating lease, right-of-use assets	$ 29,404
Operating lease, liabilities	29,404
Leasing cost	$ 2,200
Minimum
Accounting Policies [Line Items]
Observatory revenue realized during the first quarter, previous ten years (as a percent)	16.00%
Observatory revenue realized during the second quarter, previous ten years (as a percent)	26.00%
Observatory revenue realized during the third quarter, previous ten years (as a percent)	31.00%
Observatory revenue realized during the fourth quarter, previous ten years (as a percent)	23.00%
Maximum
Accounting Policies [Line Items]
Observatory revenue realized during the first quarter, previous ten years (as a percent)	18.00%
Observatory revenue realized during the second quarter, previous ten years (as a percent)	28.00%
Observatory revenue realized during the third quarter, previous ten years (as a percent)	33.00%
Observatory revenue realized during the fourth quarter, previous ten years (as a percent)	25.00%
ASU 2016-02
Accounting Policies [Line Items]
Operating lease, right-of-use assets		$ 29,500
Operating lease, liabilities		$ 29,500