Derivative Instruments and Hedging Activities - Summary of Outstanding Interest Rate Swaps (Details) - USD ($)	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Derivative [Line Items]
Interest rate swap assets	$ 1,375,000	$ 139,000
Interest rate swap liabilities	1,726,000	22,446,000
Designated as Hedging Instrument [Member] | 1633 Broadway [Member] | Cash Flow Hedges [Member]
Derivative [Line Items]
Aggregate notional amount		$ 400,000,000
Effective Dates, Liabilities		2015-12
Maturity Date, Liabilities		2020-12
Strike Rate, Liabilities		1.65%
Designated as Hedging Instrument [Member] | 1633 Broadway [Member] | Cash Flow Hedges [Member] | Other Assets [Member]
Derivative [Line Items]
Interest rate swap assets	1,375,000	$ 139,000
Designated as Hedging Instrument [Member] | 1633 Broadway [Member] | Interest Rate Swap Two Thousand Fifteen to Two Thousand Twenty [Member] | Cash Flow Hedges [Member]
Derivative [Line Items]
Notional Amount, Assets	$ 400,000,000
Effective Dates, Assets	2015-12
Maturity Date, Assets	2020-12
Strike Rate, Assets	1.65%
Interest rate swap assets	$ 1,233,000
Interest rate swap liabilities		12,000
Designated as Hedging Instrument [Member] | 1633 Broadway [Member] | Interest Rate Swap Two Thousand Fifteen to Two Thousand Twenty One [Member] | Cash Flow Hedges [Member]
Derivative [Line Items]
Notional Amount, Assets	$ 300,000,000
Effective Dates, Assets	2015-12
Maturity Date, Assets	2021-12
Strike Rate, Assets	1.82%
Interest rate swap assets	$ 142,000
Interest rate swap liabilities		379,000
Designated as Hedging Instrument [Member] | 1633 Broadway [Member] | Interest Rate Swap Two Thousand Twenty to Two Thousand Twenty One [Member] | Cash Flow Hedges [Member]
Derivative [Line Items]
Notional Amount, Assets		$ 400,000,000
Effective Dates, Assets		2020-12
Maturity Date, Assets		2021-12
Strike Rate, Assets		2.35%
Interest rate swap assets		$ 139,000
Aggregate notional amount	$ 400,000,000
Effective Dates, Liabilities	2020-12
Maturity Date, Liabilities	2021-12
Strike Rate, Liabilities	2.35%
Interest rate swap liabilities	$ 921,000
Designated as Hedging Instrument [Member] | 1633 Broadway [Member] | Interest Rate Swap Two Thousand Fifteen to Two Thousand Twenty Two [Member] | Cash Flow Hedges [Member]
Derivative [Line Items]
Aggregate notional amount	$ 300,000,000
Effective Dates, Liabilities	2015-12
Maturity Date, Liabilities	2022-12
Strike Rate, Liabilities	1.95%
Interest rate swap liabilities	$ 805,000	828,000
Designated as Hedging Instrument [Member] | 1633 Broadway [Member] | Interest Rate Swap September Two Thousand Fifteen [Member] | Cash Flow Hedges [Member]
Derivative [Line Items]
Aggregate notional amount		$ 300,000,000
Effective Dates, Liabilities		2015-12
Maturity Date, Liabilities		2022-12
Strike Rate, Liabilities		1.95%
Designated as Hedging Instrument [Member] | 1633 Broadway [Member] | Interest Rate Swap November Two Thousand Fifteen [Member] | Cash Flow Hedges [Member]
Derivative [Line Items]
Aggregate notional amount		$ 300,000,000
Effective Dates, Liabilities		2015-12
Maturity Date, Liabilities		2021-12
Strike Rate, Liabilities		1.82%
Designated as Hedging Instrument [Member] | 1633 Broadway [Member] | Interest Rate Swap [Member] | Cash Flow Hedges [Member]
Derivative [Line Items]
Aggregate notional amount	1,000,000,000
Interest rate swap liabilities	$ 1,726,000	$ 1,219,000