Subsequent Event - Preferred Stock (Details) - Subsequent event - Series A Preferred Stock - Development Bank of Japan Inc. $ / shares in Units, $ in Millions	Oct. 11, 2016 USD ($) $ / shares shares
Subsequent events
Sale and issuance of shares | shares	1,000,000
Dividend rate (as a percent)	6.50%
Preferred stock, par value (in dollars per share)	$ 0.01
Purchase price (in dollars per share)	20.00
Preferred stock liquidation preference (in dollars per share)	$ 20.00
Net proceeds from preferred stock | $	$ 19.8