Debt - Credit Facilities (Details) - Line of Credit - USD ($)	Dec. 05, 2018	Dec. 19, 2014	Dec. 31, 2018
Fifth Amended and Restated Credit Agreement
Line of Credit Facility [Line Items]
Percentage of loan availability from pledged assets from mortgaged assets, maximum	10.00%
Borrowings outstanding			$ 0
Letters of credit outstanding			66,100,000
Revolving Credit Facility | Fifth Amended and Restated Credit Agreement
Line of Credit Facility [Line Items]
Credit Facility, maximum borrowing capacity	$ 250,000,000
Current borrowing capacity			179,400,000
Letter of credit sublimit | Fifth Amended and Restated Credit Agreement
Line of Credit Facility [Line Items]
Credit Facility, maximum borrowing capacity	60,000,000
Letters of credit outstanding			40,700,000
Swingline Line of Credit | Fifth Amended and Restated Credit Agreement
Line of Credit Facility [Line Items]
Credit Facility, maximum borrowing capacity	50,000,000
Option to increase maximum borrowing capacity | Fifth Amended and Restated Credit Agreement
Line of Credit Facility [Line Items]
Credit Facility, maximum borrowing capacity	$ 100,000,000
Letter of Credit | Fifth Amended and Restated Credit Agreement
Line of Credit Facility [Line Items]
Credit Facility, maximum borrowing capacity			$ 66,200,000
LIBOR | Minimum | Fifth Amended and Restated Credit Agreement
Line of Credit Facility [Line Items]
Basis spread on variable rate basis	2.25%
LIBOR | Minimum | Fourth Amended and Restated Credit Agreement
Line of Credit Facility [Line Items]
Basis spread on variable rate basis		2.50%
LIBOR | Maximum | Fifth Amended and Restated Credit Agreement
Line of Credit Facility [Line Items]
Basis spread on variable rate basis	3.25%
LIBOR | Maximum | Fourth Amended and Restated Credit Agreement
Line of Credit Facility [Line Items]
Basis spread on variable rate basis		3.50%
Applicable Margin, Less Than Or Equal To 35% Utilization | Fifth Amended and Restated Credit Agreement
Line of Credit Facility [Line Items]
Facility utilization percentage	35.00%
Applicable Margin, Less Than Or Equal To 35% Utilization | LIBOR | Fifth Amended and Restated Credit Agreement
Line of Credit Facility [Line Items]
Basis spread on variable rate basis	2.25%
Applicable Margin, Greater Than 35% But Less Than Or Equal To 50% Utilization | Minimum | Fifth Amended and Restated Credit Agreement
Line of Credit Facility [Line Items]
Facility utilization percentage	35.00%
Applicable Margin, Greater Than 35% But Less Than Or Equal To 50% Utilization | Maximum | Fifth Amended and Restated Credit Agreement
Line of Credit Facility [Line Items]
Facility utilization percentage	50.00%
Applicable Margin, Greater Than 35% But Less Than Or Equal To 50% Utilization | LIBOR | Fifth Amended and Restated Credit Agreement
Line of Credit Facility [Line Items]
Basis spread on variable rate basis	2.75%
Applicable Margin, Greater Than 50% Utilization | Fifth Amended and Restated Credit Agreement
Line of Credit Facility [Line Items]
Facility utilization percentage	50.00%
Applicable Margin, Greater Than 50% Utilization | LIBOR | Fifth Amended and Restated Credit Agreement
Line of Credit Facility [Line Items]
Basis spread on variable rate basis	3.25%
Unused Commitment Fee, Outstanding Debt Percentage Greater Than Or Equal To 50% | Fifth Amended and Restated Credit Agreement
Line of Credit Facility [Line Items]
Quarterly commitment fee	0.25%
Line of credit percentage outstanding	50.00%
Unused Commitment Fee, Outstanding Debt Percentage Less Than 50% | Fifth Amended and Restated Credit Agreement
Line of Credit Facility [Line Items]
Quarterly commitment fee	0.35%
Line of credit percentage outstanding	50.00%