Significant Transactions During the Three Months Ended 2018 and Subsequent Events (Details) - USD ($)	1 Months Ended
	Mar. 31, 2018	Jan. 31, 2018
Other Commitments [Line Items]
Proceeds from full redemption of a preferred equity investment in a joint venture		$ 2,400,000
Promote income	$ 20,500,000
Stock repurchased and retired during the period (in shares)		16,834
Stock repurchased and retired during the period		$ 3,800,000
Purchase authority remaining under stock repurchase plan	245,200,000
Senior Notes [Member] | Senior Unsecured Notes At 4.500% [Member]
Other Commitments [Line Items]
Debt, face amount	$ 300,000,000
Debt, term (in years)	30 years
Debt, stated interest rate	4.50%
BEX III [Member]
Other Commitments [Line Items]
Repayments of related party debt		$ 29,500,000