Notes and Bonds Payable - Narrative (Details)						2 Months Ended	3 Months Ended	12 Months Ended
	Dec. 27, 2017 USD ($)	Nov. 01, 2017 USD ($)	Jul. 05, 2016 USD ($)	Apr. 24, 2015 USD ($) swap_agreement	Feb. 15, 2013 extension_option	Dec. 31, 2017 USD ($) swap_agreement	Dec. 31, 2017 USD ($) swap_agreement	Dec. 31, 2017 USD ($) swap_agreement	Dec. 31, 2016 USD ($) swap_agreement	Dec. 31, 2015 USD ($) swap_agreement	Jan. 30, 2018 USD ($) swap_agreement derivative	Dec. 20, 2017 USD ($) swap_agreement	Dec. 18, 2017 Lender	Dec. 11, 2017 USD ($)	Feb. 28, 2014 USD ($) Lender	Mar. 26, 2013 USD ($)	Oct. 14, 2011 USD ($)
Debt Instrument [Line Items]
Number of interest rate swaps | swap_agreement						2	2	2
Unsecured term loan outstanding						$ 1,293,916,000	$ 1,293,916,000	$ 1,293,916,000
Interest paid								64,395,000	$ 55,878,000	$ 69,773,000
Loss on extinguishment of debt							45,000,000	$ (44,985,000)		$ (27,998,000)
Number of forward starting swaps | swap_agreement								4	4	4
Subsequent Event [Member]
Debt Instrument [Line Items]
Number of interest rate swaps | derivative											2
Line of Credit [Member] | Unsecured Credit Facility [Member]
Debt Instrument [Line Items]
Unsecured credit facility																	$ 700,000,000.0
Number of extension options | extension_option					2
Period of extension option					6 months
Extension fees as percentage of aggregate commitments					0.075%
Facility fee on the aggregate amount of commitments								0.20%
Amount outstanding under Unsecured Credit Facility						$ 189,000,000	$ 189,000,000	$ 189,000,000
Weighted average interest rate (LOC)						2.56%	2.56%	2.56%
Remaining borrowing capacity						$ 511,000,000	$ 511,000,000	$ 511,000,000
Line of Credit [Member] | Unsecured Credit Facility [Member] | Minimum [Member]
Debt Instrument [Line Items]
Facility fee on the aggregate amount of commitments								0.13%
Line of Credit [Member] | Unsecured Credit Facility [Member] | Maximum [Member]
Debt Instrument [Line Items]
Facility fee on the aggregate amount of commitments								0.30%
Line of Credit [Member] | Unsecured Credit Facility [Member] | LIBOR [Member]
Debt Instrument [Line Items]
Percentage of interest in addition to LIBOR								1.00%
Contractual interest rates, basis spread on variable rate								1.00%
Line of Credit [Member] | Unsecured Credit Facility [Member] | LIBOR [Member] | Minimum [Member]
Debt Instrument [Line Items]
Percentage of interest in addition to LIBOR								0.83%
Line of Credit [Member] | Unsecured Credit Facility [Member] | LIBOR [Member] | Maximum [Member]
Debt Instrument [Line Items]
Percentage of interest in addition to LIBOR								1.55%
Medium-term Notes [Member] | Term Loan due 2022 [Member]
Debt Instrument [Line Items]
Weighted average interest rate (LOC)						2.77%	2.77%	2.77%
Senior notes face value															$ 200,000,000.0
Number of lenders, term loan | Lender													9		9
Amount of debt repaid			$ 50,000,000
Contractual interest rates, basis spread on variable rate								1.10%
Number of interest rate swaps | swap_agreement												2
Unsecured term loan outstanding						$ 150,000,000	$ 150,000,000	$ 150,000,000
Medium-term Notes [Member] | Term Loan due 2022 [Member] | Subsequent Event [Member]
Debt Instrument [Line Items]
Number of interest rate swaps | swap_agreement											2
Derivative notional amount											$ 50,000,000
Derivative, fixed interest rate											2.46%
Medium-term Notes [Member] | Term Loan due 2022 [Member] | Interest Rate Swap [Member]
Debt Instrument [Line Items]
Derivative notional amount												$ 25,000,000
Derivative, fixed interest rate												2.18%
Medium-term Notes [Member] | Term Loan due 2022 [Member] | Minimum [Member]
Debt Instrument [Line Items]
Contractual interest rates, basis spread on variable rate								0.90%
Medium-term Notes [Member] | Term Loan due 2022 [Member] | Maximum [Member]
Debt Instrument [Line Items]
Contractual interest rates, basis spread on variable rate								1.75%
Medium-term Notes [Member] | Term Loan due 2022 [Member] | LIBOR [Member]
Debt Instrument [Line Items]
Contractual interest rates, basis spread on variable rate								1.10%
Senior Notes [Member] | Senior Notes due 2021 [Member]
Debt Instrument [Line Items]
Senior notes face value						0	0	$ 0	$ 400,000,000
Amount of debt repaid	$ 300,000,000	$ 100,000,000				400,000,000	$ 400,000,000
Extinguishment of debt, number of transactions							2
Aggregate redemption price of debt						452,300,000
Interest paid						9,500,000
Make-whole payment on early extinguishment of debt						42,800,000
Write off of unamortized deferred financing costs						2,200,000
Loss on extinguishment of debt						$ 45,000,000
Interest rate on senior notes						5.75%	5.75%	5.75%
Unaccreted discount						$ 0	$ 0	$ 0	1,510,000
Senior Notes [Member] | Senior Notes due 2023 [Member]
Debt Instrument [Line Items]
Senior notes face value						$ 250,000,000	$ 250,000,000	$ 250,000,000	250,000,000							$ 250,000,000.0
Interest rate on senior notes						3.75%	3.75%	3.75%								3.75%
Unaccreted discount						$ 1,178,000	$ 1,178,000	$ 1,178,000	1,375,000							$ 2,100,000
Deferred finance costs, gross																$ 2,100,000
Interest rate yielded per annum upon issuance																3.95%
Amount of amortization included in interest expense on the Company's consolidated Statements of operations								200,000	200,000	$ 200,000
Amortization of debt issuance costs								200,000	200,000	200,000
Senior Notes [Member] | Senior Notes due 2025 [Member]
Debt Instrument [Line Items]
Senior notes face value				$ 250,000,000.0		$ 250,000,000	$ 250,000,000	$ 250,000,000	250,000,000
Interest rate on senior notes				3.875%		3.88%	3.88%	3.88%
Unaccreted discount				$ 200,000		$ 160,000	$ 160,000	$ 160,000	178,000
Deferred finance costs, gross				$ 2,300,000
Interest rate yielded per annum upon issuance				4.08%
Amortization of debt issuance costs								200,000	200,000	100,000
Number of forward starting swaps | swap_agreement				4
Senior Notes [Member] | Senior Notes due 2025 [Member] | Interest Rate Swap [Member]
Debt Instrument [Line Items]
Loss on forward starting interest rate swap agreements recognized in OCI				$ 1,700,000
Senior Notes [Member] | Senior Notes due 2028 [Member]
Debt Instrument [Line Items]
Senior notes face value						$ 300,000,000	$ 300,000,000	$ 300,000,000						$ 300,000,000.0
Interest rate on senior notes						3.63%	3.63%	3.63%						3.625%
Unaccreted discount						$ 2,529,000	$ 2,529,000	$ 2,529,000						$ 2,500,000
Deferred finance costs, gross														$ 2,700,000
Interest rate yielded per annum upon issuance														3.84%
Mortgage Notes [Member] | Minimum [Member]
Debt Instrument [Line Items]
Interest rate on senior notes						3.30%	3.30%	3.30%
Mortgage Notes [Member] | Maximum [Member]
Debt Instrument [Line Items]
Interest rate on senior notes						6.90%	6.90%	6.90%
Mortgage Notes [Member] | Mortgage notes payable [Member]
Debt Instrument [Line Items]
Senior notes face value						$ 154,916,000	$ 154,916,000	$ 154,916,000	114,934,000
Unaccreted discount						$ 1,332,000	$ 1,332,000	1,332,000	1,450,000
Amortization of debt issuance costs								100,000	200,000	200,000
Amortization of debt discount								300,000	300,000	800,000
Amortization of debt premium								$ 700,000	$ 900,000	$ 1,000,000
Mortgage Notes [Member] | Mortgage notes payable [Member] | Minimum [Member]
Debt Instrument [Line Items]
Interest rate on senior notes						3.31%	3.31%	3.31%
Mortgage Notes [Member] | Mortgage notes payable [Member] | Maximum [Member]
Debt Instrument [Line Items]
Interest rate on senior notes						6.88%	6.88%	6.88%