Subsequent Events (Details) - Unsecured Debt [Member] - Subsequent Event [Member] $ in Millions	Aug. 01, 2016 USD ($)
senior unsecured private placement notes payable, 4.35 percent, due August 22, 2024 [Member]
Subsequent Event [Line Items]
Debt Instrument, Face Amount	$ 148.0
Long-term Debt, Percentage Bearing Fixed Interest, Percentage Rate	4.35%
senior unsecured private placement notes payable, 4.56 percent, due August 22, 2026 [Member]
Subsequent Event [Line Items]
Debt Instrument, Face Amount	$ 192.0
Long-term Debt, Percentage Bearing Fixed Interest, Percentage Rate	4.56%
Private Placement [Member]
Subsequent Event [Line Items]
Debt Instrument, Face Amount	$ 340.0