Short-Term Borrowings (Details) - USD ($)	1 Months Ended	6 Months Ended
	Dec. 31, 2015	Jun. 30, 2017	Dec. 31, 2016	Oct. 31, 2015
Short-term Debt [Line Items]
Short-term borrowings		$ 439,140,000	$ 525,842,000
Interest rates on short-term borrowings outstanding		2.21%	1.77%
Floating Rate Puttable Notes [Member]
Short-term Debt [Line Items]
Short-term borrowings		$ 102,339,000	$ 96,455,000
Equity-linked Notes [Member]
Short-term Debt [Line Items]
Short-term borrowings		28,044,000	0
Proceeds from debt		30,600,000
Bank loans [Member]
Short-term Debt [Line Items]
Short-term borrowings		308,757,000	372,301,000
Revolving Credit Facility [Member]
Short-term Debt [Line Items]
Short-term borrowings		$ 0
Revolving Credit Facility [Member] | Secured Revolving Loan Facility [Member]
Short-term Debt [Line Items]
Short-term borrowings			$ 57,086,000
Credit facility maximum amount				$ 50,000,000.0
Revolving Credit Facility [Member] | Secured Revolving Loan Facility [Member] | London Interbank Offered Rate (LIBOR) [Member]
Short-term Debt [Line Items]
Debt instrument, basic spread on variable rate		3.75%
Revolving Credit Facility [Member] | Loan Facility [Member] | London Interbank Offered Rate (LIBOR) [Member]
Short-term Debt [Line Items]
Debt instrument, basic spread on variable rate	4.25%
Line of Credit [Member] | Loan Facility [Member]
Short-term Debt [Line Items]
Credit facility maximum amount	$ 50,000,000.0
Line of Credit [Member] | Intraday Credit Facility [Member]
Short-term Debt [Line Items]
Credit facility maximum amount		$ 250,000,000.0
Line of Credit [Member] | Intraday Credit Facility [Member] | Federal Funds Effective Swap Rate [Member]
Short-term Debt [Line Items]
Debt instrument, basic spread on variable rate		0.50%