Debt - Narrative (Details) - USD ($)	1 Months Ended	3 Months Ended
	Feb. 28, 2019	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Line of Credit Facility [Line Items]
Letters of credit outstanding		$ 2,300,000		$ 0
Repayments of debt		70,614,000	$ 592,000
Estimated fair value of debt		165,100,000		164,300,000
Unrealized gain (loss) on derivative instruments		(9,039,000)	5,278,000
Interest rate swaps
Line of Credit Facility [Line Items]
Derivative instruments, asset position, fair value		11,100,000
Derivative instruments, liability position, fair value		6,800,000
Unrealized gain (loss) on derivative instruments		(9,000,000)	5,300,000
Expected reclassifications in next 12 months		1,200,000
Interest rate swaps | Interest expense
Line of Credit Facility [Line Items]
Reclassification of gain (loss) from AOCI to interest expense		(2,500,000)	$ 300,000
Letters of credit
Line of Credit Facility [Line Items]
Maximum borrowing capacity		30,000,000
Unsecured debt | Revolving credit facilities
Line of Credit Facility [Line Items]
Debt outstanding		0		170,000,000
Unsecured debt | Unsecured term loans
Line of Credit Facility [Line Items]
Debt outstanding		2,355,000,000		2,425,000,000
Unsecured debt | Senior unsecured credit facility | Revolving credit facilities
Line of Credit Facility [Line Items]
Maximum borrowing capacity		650,000,000
Debt outstanding		0		170,000,000
Remaining borrowing capacity		650,000,000
Maximum borrowing capacity potential increase (up to)		$ 1,300,000,000.0
Unsecured debt | Senior unsecured credit facility | Revolving credit facilities | Minimum
Line of Credit Facility [Line Items]
Unused commitment fee annual rate		0.20%
Unsecured debt | Senior unsecured credit facility | Revolving credit facilities | Minimum | LIBOR
Line of Credit Facility [Line Items]
Credit facility borrowings LIBOR rate plus		1.45%
Unsecured debt | Senior unsecured credit facility | Revolving credit facilities | Maximum
Line of Credit Facility [Line Items]
Unused commitment fee annual rate		0.30%
Unsecured debt | Senior unsecured credit facility | Revolving credit facilities | Maximum | LIBOR
Line of Credit Facility [Line Items]
Credit facility borrowings LIBOR rate plus		2.25%
Unsecured debt | PHL unsecured credit facility | Revolving credit facilities
Line of Credit Facility [Line Items]
Maximum borrowing capacity		$ 10,000,000
Debt outstanding		0		0
Remaining borrowing capacity		$ 10,000,000
Unsecured debt | PHL unsecured credit facility | Revolving credit facilities | Minimum | LIBOR
Line of Credit Facility [Line Items]
Credit facility borrowings LIBOR rate plus		1.45%
Unsecured debt | PHL unsecured credit facility | Revolving credit facilities | Maximum | LIBOR
Line of Credit Facility [Line Items]
Credit facility borrowings LIBOR rate plus		2.25%
Unsecured debt | Sixth Term Loan Tranche 2020 | Unsecured term loans
Line of Credit Facility [Line Items]
Debt outstanding		$ 180,000,000		250,000,000
Repayments of debt	$ 70,000,000
Senior unsecured notes
Line of Credit Facility [Line Items]
Debt outstanding		100,000,000		100,000,000
Senior unsecured notes | Series A Notes
Line of Credit Facility [Line Items]
Debt outstanding		$ 60,000,000		60,000,000
Stated interest rate		4.70%
Senior unsecured notes | Series B Notes
Line of Credit Facility [Line Items]
Debt outstanding		$ 40,000,000		$ 40,000,000
Stated interest rate		4.93%