Credit Facility (Details)		12 Months Ended
	Jan. 07, 2015 USD ($)	Dec. 31, 2015 USD ($)
Unsecured Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Credit facility term	5 years
Unsecured credit facility maximum amount	$ 250,000,000
Potential increase in revolving credit facility commitment	$ 250,000,000
Consolidated leverage ratio (note more than)	3.5
Consolidated interest coverage ratio (not less than)	3.0
Line of Credit [Member]
Line of Credit Facility [Line Items]
Weighted average interest rate (percent)		1.82%
Amount outstanding		$ 0
Line of Credit [Member] | Letter of Credit [Member]
Line of Credit Facility [Line Items]
Unsecured credit facility maximum amount	$ 25,000,000.0
Line of Credit [Member] | Swing Line Loans [Member]
Line of Credit Facility [Line Items]
Unsecured credit facility maximum amount	$ 10,000,000.0
London Interbank Offered Rate (LIBOR) [Member] | Line of Credit [Member]
Line of Credit Facility [Line Items]
Basis spread on LIBOR (percent)		1.10%
Minimum | Line of Credit [Member]
Line of Credit Facility [Line Items]
Quarterly facility fee (percent)		0.125%
Minimum | London Interbank Offered Rate (LIBOR) [Member] | Line of Credit [Member]
Line of Credit Facility [Line Items]
Basis spread on LIBOR (percent)		1.00%
Maximum | Line of Credit [Member]
Line of Credit Facility [Line Items]
Quarterly facility fee (percent)		0.20%
Maximum | London Interbank Offered Rate (LIBOR) [Member] | Line of Credit [Member]
Line of Credit Facility [Line Items]
Basis spread on LIBOR (percent)		1.30%