Stock-Based Compensation (Details 2) - Nonvested shares	12 Months Ended
	Dec. 31, 2016
2016 Performance-Based Grants | Compounded Annual Book Value Per Share Growth 13%
Stock-based compensation
Compounded Annual Book Value Per Share Growth	13.00%
Nonvested Common Shares Earned (as percent)	25.00%
2016 Performance-Based Grants | Compounded Annual Book Value Per Share Growth 14 %
Stock-based compensation
Compounded Annual Book Value Per Share Growth	14.00%
Nonvested Common Shares Earned (as percent)	50.00%
2016 Performance-Based Grants | Compounded Annual Book Value Per Share Growth 15%
Stock-based compensation
Compounded Annual Book Value Per Share Growth	15.00%
Nonvested Common Shares Earned (as percent)	75.00%
2016 Performance-Based Grants | Maximum | Compounded Annual Book Value Per Share Growth 13%
Stock-based compensation
Compounded Annual Book Value Per Share Growth	13.00%
Nonvested Common Shares Earned (as percent)	0.00%
2016 Performance-Based Grants | Minimum | Compounded Annual Book Value Per Share Growth 16 %
Stock-based compensation
Compounded Annual Book Value Per Share Growth	16.00%
Nonvested Common Shares Earned (as percent)	100.00%
2013, 2014 and 2015 Performance-Based Grants | Compounded Annual Book Value Per Share Growth 11%
Stock-based compensation
Compounded Annual Book Value Per Share Growth	11.00%
Nonvested Common Shares Earned (as percent)	10.00%
2013, 2014 and 2015 Performance-Based Grants | Compounded Annual Book Value Per Share Growth 12%
Stock-based compensation
Compounded Annual Book Value Per Share Growth	12.00%
Nonvested Common Shares Earned (as percent)	36.00%
2013, 2014 and 2015 Performance-Based Grants | Compounded Annual Book Value Per Share Growth 13%
Stock-based compensation
Compounded Annual Book Value Per Share Growth	13.00%
Nonvested Common Shares Earned (as percent)	61.00%
2013, 2014 and 2015 Performance-Based Grants | Compounded Annual Book Value Per Share Growth 14 %
Stock-based compensation
Compounded Annual Book Value Per Share Growth	14.00%
Nonvested Common Shares Earned (as percent)	87.00%
2013, 2014 and 2015 Performance-Based Grants | Maximum | Compounded Annual Book Value Per Share Growth 11%
Stock-based compensation
Compounded Annual Book Value Per Share Growth	11.00%
Nonvested Common Shares Earned (as percent)	0.00%
2013, 2014 and 2015 Performance-Based Grants | Minimum | Compounded Annual Book Value Per Share Growth 15%
Stock-based compensation
Compounded Annual Book Value Per Share Growth	15.00%
Nonvested Common Shares Earned (as percent)	100.00%