Debt - Narrative (Details)				12 Months Ended
	May 10, 2017 USD ($)	Feb. 01, 2016 USD ($) extension_option	Aug. 05, 2015 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Line of Credit Facility [Line Items]
Gross proceeds from issuance of senior notes				$ 0	$ 100,000,000	$ 0
Payments on the mortgage notes payable				0	95,022,000	3,183,000
Amount outstanding				565,000,000	455,000,000
Amount outstanding				558,912,000	449,716,000
Interest expense				24,196,000	22,873,000	24,048,000
Amortization of deferred financing costs				2,100,000	2,200,000	2,200,000
Interest payable				1,400,000	1,300,000
Loss on extinguishment of debt before write-off of deferred financing costs				(7,600,000)
Write-off of deferred financing costs				4,200,000	300,000
Loss on the extinguishment of debt				11,883,000	326,000	$ 1,208,000
Senior Unsecured Notes
Line of Credit Facility [Line Items]
Amount outstanding				300,000,000	260,000,000
Amount outstanding				294,395,000	255,294,000
Senior Unsecured Notes | 5.25% Senior Notes due 2025
Line of Credit Facility [Line Items]
Debt instrument, face amount	$ 300,000,000.0
Interest rate, stated percentage	5.25%
Gross proceeds from issuance of senior notes	$ 300,000,000
Net proceeds from issuance of senior notes	$ 294,000,000
Debt instrument, redemption price, percentage	100.00%
Debt instrument, redemption price, percentage upon change of control	101.00%
Senior Unsecured Notes | 5.25% Senior Notes due 2025 | Debt Instrument, Redemption, Period One
Line of Credit Facility [Line Items]
Debt instrument, redemption price, percentage	105.25%
Senior Unsecured Notes | 5.25% Senior Notes due 2025 | Debt Instrument, Redemption, Period One | Maximum
Line of Credit Facility [Line Items]
Debt instrument, redemption price, percentage of principal amount	40.00%
Senior Unsecured Notes | 5.25% Senior Notes due 2025 | Debt Instrument, Redemption, Period One | Minimum
Line of Credit Facility [Line Items]
Percentage of aggregate principal amount of notes outstanding	60.00%
Senior Unsecured Notes | 5.875% Senior Notes due 2021
Line of Credit Facility [Line Items]
Interest rate, stated percentage	5.875%
Payments for redemption of senior notes	$ 260,000,000
Debt instrument, redemption price, percentage	102.938%
Credit facility
Line of Credit Facility [Line Items]
Amount outstanding				165,000,000	95,000,000
Amount outstanding				165,000,000	95,000,000
Credit facility | Unsecured Revolving Credit Facility
Line of Credit Facility [Line Items]
Line of credit facility, borrowing capacity			$ 300,000,000.0
Credit facility | Revolving Credit Facility as Amended
Line of Credit Facility [Line Items]
Line of credit facility, borrowing capacity		$ 400,000,000.0
Line of credit facility, increase to borrowing capacity		100,000,000.0
Line of credit facility, increase to uncommitted incremental facility		50,000,000.0
Line of credit facility, uncommitted incremental facility limit		$ 250,000,000.0
Number of extension options | extension_option		2
Extension option term		6 months
Credit facility | Revolving Credit Facility as Amended | Maximum
Line of Credit Facility [Line Items]
Line of credit facility, commitment fee percentage			0.25%
Line of credit facility, facility fee percentage			0.30%
Credit facility | Revolving Credit Facility as Amended | Maximum | Base Rate
Line of Credit Facility [Line Items]
Debt instrument, basis spread		1.60%	1.40%
Credit facility | Revolving Credit Facility as Amended | Maximum | LIBOR
Line of Credit Facility [Line Items]
Debt instrument, basis spread		2.60%	2.40%
Credit facility | Revolving Credit Facility as Amended | Minimum
Line of Credit Facility [Line Items]
Line of credit facility, commitment fee percentage			0.15%
Line of credit facility, facility fee percentage			0.125%
Credit facility | Revolving Credit Facility as Amended | Minimum | Base Rate
Line of Credit Facility [Line Items]
Debt instrument, basis spread		0.95%	0.75%
Credit facility | Revolving Credit Facility as Amended | Minimum | LIBOR
Line of Credit Facility [Line Items]
Debt instrument, basis spread		1.95%	1.75%
Senior Unsecured Term Loan [Member]
Line of Credit Facility [Line Items]
Line of credit facility, prepayment premium in first year		2.00%
Line of credit facility, prepayment premium in second year		1.00%
Amount outstanding		$ 100,000,000		100,000,000	100,000,000
Amount outstanding				$ 99,517,000	$ 99,422,000
Mortgage Notes Payable
Line of Credit Facility [Line Items]
Payments on the mortgage notes payable		$ 95,000,000