Debt (Details Textual)	Mar. 31, 2016 USD ($)
Line of credit
Line of Credit Facility [Line Items]
Total borrowing capacity under lines of credit	$ 873,700,000
Total available for borrowings under lines of credit	538,600,000
Line of credit | Secured Debt
Line of Credit Facility [Line Items]
Total borrowing capacity under lines of credit	23,700,000
Senior Notes
Line of Credit Facility [Line Items]
Face amount of debt	75,000,000
Notes Payable, due 2021 | Senior Notes
Line of Credit Facility [Line Items]
Face amount of debt	$ 26,000,000.0
Interest rate	4.10%
Notes Payable, due 2023 | Senior Notes
Line of Credit Facility [Line Items]
Face amount of debt	$ 24,000,000.0
Interest rate	4.60%
Notes Payable, due 2026 | Senior Notes
Line of Credit Facility [Line Items]
Face amount of debt	$ 25,000,000.0
Interest rate	4.90%