Preferred Stock Preferred Stock (Details)	12 Months Ended
	Dec. 31, 2017 class_of_stock quarter
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Number of authorized classes of preferred stock (class of stock) | class_of_stock	2
Minimum number of quarters dividends are paid in arrears (minimum of 6 quarters) | quarter	6