Fair Value Measurement - Narrative (Details)	12 Months Ended
	Dec. 31, 2016 USD ($) Agreement Receivable	Dec. 31, 2015 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Number of unsecured receivables | Receivable	2
Number of line of credit agreements | Agreement	2
Transfers between Level 2 to Level 1		$ 0
Equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities transferred from Level 2 to Level 1	$ 10,200,000
Transfers between Level 1 to Level 2		$ 0
A- Rating | Corporate debt, limited observable inputs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Credit rating		83.00%
BBB Plus Rating | Corporate debt, limited observable inputs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Credit rating	84.00%