Line of Credit (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Apr. 16, 2017	Jan. 18, 2017	Sep. 19, 2016
Line of Credit Facility [Line Items]
Credit line outstanding	$ 49,987,000	$ 50,000,000
Total interest expense on borrowings	$ 1,300,000	$ 300,000	$ 23,000
Line of Credit
Line of Credit Facility [Line Items]
Maximum borrowing capacity						$ 85,000,000.0
Line of Credit | US Bank
Line of Credit Facility [Line Items]
Effective interest rate	1.89%
Commitment fees	$ 0
Line of Credit | US Bank | London Interbank Offered Rate (LIBOR) | Minimum
Line of Credit Facility [Line Items]
Basis spread on variable rate	1.25%
Line of Credit | US Bank | London Interbank Offered Rate (LIBOR) | Maximum
Line of Credit Facility [Line Items]
Basis spread on variable rate	1.75%
Line of Credit | US Bank | Base rate | Minimum
Line of Credit Facility [Line Items]
Basis spread on variable rate	0.00%
Line of Credit | US Bank | Base rate | Maximum
Line of Credit Facility [Line Items]
Basis spread on variable rate	0.50%
Line of Credit | US Bank | Enson
Line of Credit Facility [Line Items]
Subsidiary ownership percentage securing facility	65.00%
Line of Credit | Forecast
Line of Credit Facility [Line Items]
Maximum borrowing capacity				$ 85,000,000.0
Line of Credit | Subsequent event
Line of Credit Facility [Line Items]
Maximum borrowing capacity					$ 105,000,000.0
Letter of Credit
Line of Credit Facility [Line Items]
Letter of credit outstanding amount	$ 13,000