Equity, Capital and Other Interests - Other - Additional Information (Details) - shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Equity Capital And Other Interests [Abstract]
Additional common shares authorized	13,000,000
Stock repurchase program, number of shares authorized to be repurchased	13,000,000
Stock repurchased and retired during period, shares	0	0