Notes and Bonds Payable - Narrative (Details)			1 Months Ended	2 Months Ended	12 Months Ended
	Apr. 24, 2015 USD ($) swap_agreement	Feb. 15, 2013 USD ($) extension_option	Feb. 28, 2014 USD ($) Lender	Feb. 15, 2013 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($) swap_agreement	Dec. 31, 2014 USD ($)	Jul. 29, 2016 Lender	Jul. 05, 2016 USD ($)	Mar. 26, 2013 USD ($)	Oct. 14, 2011 USD ($) Lender	Dec. 13, 2010 USD ($)
Debt Instrument [Line Items]
Unsecured term loan outstanding					$ 1,271,934,000
Notes and bonds payable					1,264,370,000	$ 1,424,992,000
Unamortized discount (premium)					$ 1,944,000
Number of forward starting swaps | swap_agreement	4					4
Unsecured Credit Facility Due 2020 [Member] | Line of Credit [Member]
Debt Instrument [Line Items]
Write off of unamortized deferred financing costs				$ 100,000
Line of Credit [Member] | Unsecured Credit Facility Due 2020 [Member]
Debt Instrument [Line Items]
Unsecured credit facility											$ 700,000,000.0
Number of lenders of unsecured credit facility | Lender								14			17
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					$ 107,000,000
Weighted average interest rate (LOC)					1.80%
Remaining borrowing capacity					$ 593,000,000
Notes and bonds payable					107,000,000	$ 206,000,000
Line of Credit [Member] | Unsecured Credit Facility Due 2020 [Member] | Minimum [Member]
Debt Instrument [Line Items]
Facility fee on the aggregate amount of commitments		0.13%
Line of Credit [Member] | Unsecured Credit Facility Due 2020 [Member] | Maximum [Member]
Debt Instrument [Line Items]
Facility fee on the aggregate amount of commitments		0.30%
Deferred finance costs, gross		$ 4,400,000		$ 4,400,000
Medium-term Notes [Member] | Unsecured Term Loan Due 2019 [Member]
Debt Instrument [Line Items]
Weighted average interest rate (LOC)						1.80%
Senior notes face value			$ 200,000,000.0
Number of lenders, term loan | Lender			9
Contractual interest rates, basis spread on variable rate						1.20%
Principal repaid									$ 50,000,000
Unsecured term loan outstanding					150,000,000
Notes and bonds payable					149,491,000	$ 199,257,000
Medium-term Notes [Member] | Unsecured Term Loan Due 2019 [Member] | Minimum [Member]
Debt Instrument [Line Items]
Contractual interest rates, basis spread on variable rate			1.00%
Medium-term Notes [Member] | Unsecured Term Loan Due 2019 [Member] | Maximum [Member]
Debt Instrument [Line Items]
Contractual interest rates, basis spread on variable rate			1.95%
Senior Notes [Member] | 5.750% Senior Notes Due 2021 [Member]
Debt Instrument [Line Items]
Deferred finance costs, gross												$ 3,300,000
Senior notes face value					400,000,000	400,000,000						$ 400,000,000.0
Notes and bonds payable					$ 397,147,000	396,489,000
Interest rate on senior notes					5.75%							5.75%
Unamortized discount (premium)												$ 3,200,000
Interest rate yielded per annum upon issuance												5.97%
Amount of amortization included in interest expense on the Company's consolidated Statements of operations					$ 300,000	300,000	$ 300,000
Amortization of debt issuance costs					300,000	300,000	300,000
Unaccreted discount					1,510,000	1,832,000
Senior Notes [Member] | 3.75% Senior Notes Due 2023 [Member]
Debt Instrument [Line Items]
Deferred finance costs, gross										$ 2,100,000
Senior notes face value					250,000,000	250,000,000				$ 250,000,000.0
Notes and bonds payable					$ 247,296,000	246,897,000
Interest rate on senior notes					3.75%					3.75%
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
Unaccreted discount					1,375,000	1,565,000				$ 2,100,000
Senior Notes [Member] | 3.875% Unsecured Senior Notes due 2025 [Member]
Debt Instrument [Line Items]
Deferred finance costs, gross	$ 2,300,000
Senior notes face value	$ 250,000,000.0				250,000,000	250,000,000
Notes and bonds payable					247,819,000	247,602,000
Interest rate on senior notes	3.875%
Interest rate yielded per annum upon issuance	4.08%
Amortization of debt issuance costs					200,000	100,000
Unaccreted discount	$ 200,000				178,000	196,000
Mortgage notes payable [Member]
Debt Instrument [Line Items]
Senior notes face value					114,934,000	128,161,000
Notes and bonds payable					115,617,000	128,747,000
Amortization of debt issuance costs					200,000	200,000	200,000
Unaccreted discount					1,450,000	1,779,000
Amortization of debt discount					300,000	800,000	1,100,000
Amortization of debt premium					$ 900,000	1,000,000	$ 1,000,000
Mortgage notes payable [Member] | Minimum [Member]
Debt Instrument [Line Items]
Interest rate on senior notes					3.60%
Mortgage notes payable [Member] | Maximum [Member]
Debt Instrument [Line Items]
Interest rate on senior notes					6.88%
LIBOR [Member] | Line of Credit [Member] | Unsecured Credit Facility Due 2020 [Member]
Debt Instrument [Line Items]
Percentage of interest in addition to LIBOR					1.00%
Contractual interest rates, basis spread on variable rate					1.00%
LIBOR [Member] | Line of Credit [Member] | Unsecured Credit Facility Due 2020 [Member] | Minimum [Member]
Debt Instrument [Line Items]
Percentage of interest in addition to LIBOR		0.83%
LIBOR [Member] | Line of Credit [Member] | Unsecured Credit Facility Due 2020 [Member] | Maximum [Member]
Debt Instrument [Line Items]
Percentage of interest in addition to LIBOR		1.55%
LIBOR [Member] | Medium-term Notes [Member] | Unsecured Term Loan Due 2019 [Member]
Debt Instrument [Line Items]
Contractual interest rates, basis spread on variable rate					1.20%
Interest Rate Swap [Member]
Debt Instrument [Line Items]
Loss on forward starting interest rate swap agreements recognized in OCI	$ 1,700,000				$ 0	$ (1,684,000)