Debt (Details Textual) - USD ($) $ in Thousands				3 Months Ended			6 Months Ended
		Jan. 05, 2016	Nov. 12, 2015	Jun. 30, 2018		Jun. 30, 2017	Jun. 30, 2018		Jun. 30, 2017	Dec. 31, 2017		Oct. 13, 2017	May 17, 2017	Jun. 10, 2015	Apr. 13, 2015	Apr. 12, 2015
Line of Credit Facility [Line Items]
Outstanding borrowings under the credit facility				$ 383,000			$ 383,000			$ 45,000
Borrowings under revolving credit facilities							465,373		$ 194,922
Unrealized gain (loss) on derivative instruments				2,012		$ (1,293)	7,290		811
Repayments of mortgage debt							1,175		71,170
Estimated fair value of debt				163,300			163,300			167,100
First Mortgage [Member]
Line of Credit Facility [Line Items]
Debt outstanding				69,398			69,398			70,573
Interest Rate Swap [Member]
Line of Credit Facility [Line Items]
Derivative Asset				11,500			11,500
Unrealized gain (loss) on derivative instruments							7,290		811
Gain (Loss) on derivative instruments				0		(100)	0		0
Reclassification from AOCI to interest expense				(200)		700	100		1,800
Expected reclassifications in next 12 months				3,600			3,600
Term Loan [Member]
Line of Credit Facility [Line Items]
Debt outstanding				675,000			675,000			675,000
Unsecured Debt [Member] | Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Debt outstanding				383,000			383,000			45,000
Senior Unsecured Revolving Credit Facility [Member] | Unsecured Debt [Member]
Line of Credit Facility [Line Items]
Maximum borrowing capacity				750,000			750,000
Senior Unsecured Revolving Credit Facility [Member] | Unsecured Debt [Member] | Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Maximum borrowing capacity				450,000			450,000
Accordion feature (potential increase)				1,300,000			1,300,000
Outstanding borrowings under the credit facility				383,000			383,000			45,000
Line of credit facility, remaining borrowing capacity				67,000			67,000
Unused commitment fees				200		$ 100	400		$ 400
Debt outstanding	[1]			383,000			$ 383,000			45,000
Senior Unsecured Revolving Credit Facility [Member] | Unsecured Debt [Member] | Revolving Credit Facility [Member] | Minimum [Member]
Line of Credit Facility [Line Items]
Annual rate of unused commitment fee							0.20%
Senior Unsecured Revolving Credit Facility [Member] | Unsecured Debt [Member] | Revolving Credit Facility [Member] | Minimum [Member] | London Interbank Offered Rate (LIBOR) [Member]
Line of Credit Facility [Line Items]
Credit facility borrowings LIBOR rate plus							1.45%
Senior Unsecured Revolving Credit Facility [Member] | Unsecured Debt [Member] | Revolving Credit Facility [Member] | Maximum [Member]
Line of Credit Facility [Line Items]
Annual rate of unused commitment fee							0.30%
Senior Unsecured Revolving Credit Facility [Member] | Unsecured Debt [Member] | Revolving Credit Facility [Member] | Maximum [Member] | London Interbank Offered Rate (LIBOR) [Member]
Line of Credit Facility [Line Items]
Credit facility borrowings LIBOR rate plus							2.25%
Senior Unsecured Revolving Credit Facility [Member] | Unsecured Debt [Member] | Term Loan [Member]
Line of Credit Facility [Line Items]
Maximum borrowing capacity				300,000			$ 300,000
PHL Unsecured Revolving Credit Facility [Member] | Unsecured Debt [Member] | Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Maximum borrowing capacity													$ 10,000
Outstanding borrowings under the credit facility										0
Line of credit facility, remaining borrowing capacity				10,000			10,000
Debt outstanding	[2]			0			$ 0			0
PHL Unsecured Revolving Credit Facility [Member] | Unsecured Debt [Member] | Revolving Credit Facility [Member] | Minimum [Member]
Line of Credit Facility [Line Items]
Annual rate of unused commitment fee							0.20%
PHL Unsecured Revolving Credit Facility [Member] | Unsecured Debt [Member] | Revolving Credit Facility [Member] | Minimum [Member] | London Interbank Offered Rate (LIBOR) [Member]
Line of Credit Facility [Line Items]
Credit facility borrowings LIBOR rate plus							1.45%
PHL Unsecured Revolving Credit Facility [Member] | Unsecured Debt [Member] | Revolving Credit Facility [Member] | Maximum [Member]
Line of Credit Facility [Line Items]
Annual rate of unused commitment fee							0.30%
PHL Unsecured Revolving Credit Facility [Member] | Unsecured Debt [Member] | Revolving Credit Facility [Member] | Maximum [Member] | London Interbank Offered Rate (LIBOR) [Member]
Line of Credit Facility [Line Items]
Credit facility borrowings LIBOR rate plus							2.25%
First Term Loan [Member] | Interest Rate Swap [Member]
Line of Credit Facility [Line Items]
Notional amount				300,000			$ 300,000
First Term Loan [Member] | Term Loan [Member]
Line of Credit Facility [Line Items]
Debt outstanding	[3]			300,000			$ 300,000			300,000
First Term Loan [Member] | Term Loan [Member] | Minimum [Member] | London Interbank Offered Rate (LIBOR) [Member]
Line of Credit Facility [Line Items]
Credit facility borrowings LIBOR rate plus							1.40%
First Term Loan [Member] | Term Loan [Member] | Maximum [Member] | London Interbank Offered Rate (LIBOR) [Member]
Line of Credit Facility [Line Items]
Credit facility borrowings LIBOR rate plus							2.20%
Second Term Loan [Member]
Line of Credit Facility [Line Items]
Maximum borrowing capacity		$ 175,000		150,000			$ 150,000								$ 200,000	$ 100,000
Borrowings under revolving credit facilities		75,000
Second Term Loan [Member] | Minimum [Member] | London Interbank Offered Rate (LIBOR) [Member]
Line of Credit Facility [Line Items]
Credit facility borrowings LIBOR rate plus							1.40%
Second Term Loan [Member] | Maximum [Member] | London Interbank Offered Rate (LIBOR) [Member]
Line of Credit Facility [Line Items]
Credit facility borrowings LIBOR rate plus							2.20%
Second Term Loan [Member] | Term Loan [Member]
Line of Credit Facility [Line Items]
Debt outstanding				65,000	[3]		$ 65,000	[3]		65,000	[3]	$ 65,000
Second Term Loan, Excluded from Interest Rate Swap [Member] | Term Loan [Member]
Line of Credit Facility [Line Items]
Term loans outstanding				65,000			65,000
Fourth Term Loan [Member]
Line of Credit Facility [Line Items]
Maximum borrowing capacity				250,000			250,000
Fourth Term Loan [Member] | Interest Rate Swap [Member]
Line of Credit Facility [Line Items]
Notional amount				100,000			$ 100,000
Fourth Term Loan [Member] | Minimum [Member] | London Interbank Offered Rate (LIBOR) [Member]
Line of Credit Facility [Line Items]
Credit facility borrowings LIBOR rate plus							1.70%
Fourth Term Loan [Member] | Maximum [Member] | London Interbank Offered Rate (LIBOR) [Member]
Line of Credit Facility [Line Items]
Credit facility borrowings LIBOR rate plus							2.60%
Fourth Term Loan [Member] | Term Loan [Member]
Line of Credit Facility [Line Items]
Debt outstanding				$ 110,000	[3]		$ 110,000	[3]		110,000	[3]	$ 110,000
Fourth Term Loan [Member] | Term Loan [Member] | Interest Rate Swap [Member]
Line of Credit Facility [Line Items]
Effective interest rate				3.56%			3.56%
Fourth Term Loan Excluded From Interest Rate Swap Member [Member] | Term Loan [Member]
Line of Credit Facility [Line Items]
Term loans outstanding				$ 10,000			$ 10,000
Third Term Loan [Member]
Line of Credit Facility [Line Items]
Maximum borrowing capacity		200,000												$ 125,000
Accordion feature (potential increase)														$ 250,000
Borrowings under revolving credit facilities		$ 75,000
Third Term Loan [Member] | Interest Rate Swap [Member]
Line of Credit Facility [Line Items]
Notional amount				200,000			$ 200,000
Third Term Loan [Member] | Minimum [Member] | London Interbank Offered Rate (LIBOR) [Member]
Line of Credit Facility [Line Items]
Credit facility borrowings LIBOR rate plus							1.40%
Third Term Loan [Member] | Maximum [Member] | London Interbank Offered Rate (LIBOR) [Member]
Line of Credit Facility [Line Items]
Credit facility borrowings LIBOR rate plus							2.20%
Third Term Loan [Member] | Term Loan [Member]
Line of Credit Facility [Line Items]
Debt outstanding	[3]			$ 200,000			$ 200,000			$ 200,000
Third Term Loan [Member] | Term Loan [Member] | Interest Rate Swap [Member]
Line of Credit Facility [Line Items]
Effective interest rate				3.21%			3.21%
Series A Notes [Member]
Line of Credit Facility [Line Items]
Proceeds from issuance of senior long-term debt			$ 60,000
Stated interest rate			4.70%	4.70%			4.70%
Series B Notes [Member]
Line of Credit Facility [Line Items]
Proceeds from issuance of senior long-term debt			$ 40,000
Stated interest rate			4.93%	4.93%			4.93%
Term Loan Through July 12, 2017 [Member] | Term Loan [Member] | Interest Rate Swap [Member]
Line of Credit Facility [Line Items]
Effective interest rate				2.83%			2.83%
Term Loan July 13, 2017 through January 15, 2020 [Member] | Term Loan [Member] | Interest Rate Swap [Member]
Line of Credit Facility [Line Items]
Effective interest rate				3.46%			3.46%

[1] Borrowings bear interest at floating rates equal to, at the Company's option, either (i) LIBOR plus an applicable margin or (ii) an Adjusted Base Rate (as defined in the applicable credit agreement) plus an applicable margin.

[2] Borrowings bear interest at floating rates equal to, at the Company's option, either (i) LIBOR plus an applicable margin or (ii) an Eurocurrency Rate (as defined in the applicable credit agreement) plus an applicable margin.

[3] Borrowings under the term loan facilities bear interest at floating rates equal to, at the Company's option, either (i) LIBOR plus an applicable margin or (ii) a Base Rate plus an applicable margin. At June 30, 2018 and December 31, 2017, the Company had interest rate swaps to effectively fix the interest rate for the First Term Loan, the Third Term Loan and a portion of the Fourth Term Loan. The Company had interest rate swaps on the full amounts outstanding, except for $65.0 million on the Second Term Loan and $10.0 million on the Fourth Term Loan. See "Derivative and Hedging Activities" above.