Tax Treatment of Distributions (Details) - $ / shares |
3 Months Ended | 12 Months Ended | |||
|---|---|---|---|---|---|
Dec. 31, 2012 |
Dec. 31, 2015 |
Dec. 31, 2014 |
Dec. 31, 2013 |
Dec. 31, 2011 |
|
| Class of Stock [Line Items] | |||||
| Dividends declared per common share | $ 1.40 | $ 1.40 | $ 1.40 | ||
| Common Stock | |||||
| Class of Stock [Line Items] | |||||
| Dividends declared per common share | $ 1.400 | 1.400 | 1.400 | ||
| Less: Dividends declared in the current year and paid in the following year | (0.350) | (0.350) | (0.350) | ||
| Add: Dividends declared in the prior year and paid in the current year | 0.350 | 0.350 | 0.350 | ||
| Dividends paid per common share | $ 1.400 | $ 1.400 | $ 1.400 | $ 1.400 | |