Acquisitions - Narrative (Details) $ / shares in Units, $ in Thousands	Jul. 15, 2014 USD ($) $ / shares shares
Business Acquisition [Line Items]
Consideration paid	$ 733,600
Debt assumed	167,684
111 West 33rd Street [Member]
Business Acquisition [Line Items]
Consideration paid	423,600
Debt assumed	87,700
Payments to acquire businesses	106,900
Business combination, consideration transferred, equity interests issued and issuable	$ 229,000
Share price (USD per share) | $ / shares	$ 16.65
1400 Broadway [Member]
Business Acquisition [Line Items]
Consideration paid	$ 310,000
Debt assumed	80,000
Payments to acquire businesses	79,700
Business combination, consideration transferred, equity interests issued and issuable	$ 150,300
Share price (USD per share) | $ / shares	$ 16.65
Common Class A [Member] | 111 West 33rd Street [Member]
Business Acquisition [Line Items]
Number of shares issued (in shares) | shares	1,217,685
Common Class A [Member] | 1400 Broadway [Member]
Business Acquisition [Line Items]
Number of shares issued (in shares) | shares	1,338,488
Common Class B [Member] | 111 West 33rd Street [Member]
Business Acquisition [Line Items]
Number of shares issued (in shares) | shares	77,945
Common Class B [Member] | 1400 Broadway [Member]
Business Acquisition [Line Items]
Number of shares issued (in shares) | shares	32,452
Series PR Operating Partnership Units [Member] | 111 West 33rd Street [Member]
Business Acquisition [Line Items]
Number of shares issued (in shares) | shares	12,457,379
Share price (USD per share) | $ / shares	$ 16.65
Series PR Operating Partnership Units [Member] | 1400 Broadway [Member]
Business Acquisition [Line Items]
Number of shares issued (in shares) | shares	7,658,516
Share price (USD per share) | $ / shares	$ 16.65