Stock-Based Compensation (Details 3) - Nonvested shares	6 Months Ended
	Jun. 30, 2017
Compounded Annual Book Value Per Share Growth 16%
Stock-based compensation
Compounded Annual Book Value Per Share Growth	16.00%
Nonvested Common Shares Earned	25.00%
Compounded Annual Book Value Per Share Growth 16% | Maximum
Stock-based compensation
Compounded Annual Book Value Per Share Growth	16.00%
Nonvested Common Shares Earned	0.00%
Compounded Annual Book Value Per Share Growth 17%
Stock-based compensation
Compounded Annual Book Value Per Share Growth	17.00%
Nonvested Common Shares Earned	50.00%
Compounded Annual Book Value Per Share Growth 18%
Stock-based compensation
Compounded Annual Book Value Per Share Growth	18.00%
Nonvested Common Shares Earned	75.00%
Compounded Annual Book Value Per Share Growth 19% | Minimum
Stock-based compensation
Compounded Annual Book Value Per Share Growth	19.00%
Nonvested Common Shares Earned	100.00%