Summary Of Significant Accounting Policies Schedule of Tax Treatment Of Common Dividends Per Share For Federal Tax Purposes (Details) - $ / shares	12 Months Ended
	Dec. 31, 2016		Dec. 31, 2015		Dec. 31, 2014		Dec. 19, 2016	Jan. 28, 2016
Tax Treatment Of Common Dividends Per Share For Federal Tax Purposes [Line Items]
Dividends Payable, Amount Per Share							$ 0.75
Special dividend (per share amount)			$ 1.25		$ 4.50			$ 1.25
Dividends Treatment For Federal Tax Purposes, Percentage	100.00%		100.00%		100.00%
Dividends treatment for federal tax purposes.	$ 3.05	[1]	$ 4.04	[2]	$ 6.82	[3]
Dividend Declared
Tax Treatment Of Common Dividends Per Share For Federal Tax Purposes [Line Items]
Dividends Payable, Amount Per Share	0.75		1.90		5.15
non-special dividend
Tax Treatment Of Common Dividends Per Share For Federal Tax Purposes [Line Items]
Dividends Payable, Amount Per Share			0.65		0.65
Allocated to fiscal 2014
Tax Treatment Of Common Dividends Per Share For Federal Tax Purposes [Line Items]
Dividends Payable, Amount Per Share					4.41
Allocated to fiscal 2015
Tax Treatment Of Common Dividends Per Share For Federal Tax Purposes [Line Items]
Dividends Payable, Amount Per Share					$ 0.74
Special dividend (per share amount)			1.35
Allocated to fiscal 2016
Tax Treatment Of Common Dividends Per Share For Federal Tax Purposes [Line Items]
Special dividend (per share amount)	0.56		$ 0.55
Allocated to fiscal 2017
Tax Treatment Of Common Dividends Per Share For Federal Tax Purposes [Line Items]
Special dividend (per share amount)	$ 0.19
Capital Gains Income
Tax Treatment Of Common Dividends Per Share For Federal Tax Purposes [Line Items]
Dividends Treatment For Federal Tax Purposes, Percentage	9.49%		42.03%		100.00%
Dividends treatment for federal tax purposes.	$ 0.29		$ 1.70		$ 6.82
Ordinary Income
Tax Treatment Of Common Dividends Per Share For Federal Tax Purposes [Line Items]
Dividends Treatment For Federal Tax Purposes, Percentage	90.51%		57.97%		0.00%
Dividends treatment for federal tax purposes.	$ 2.76		$ 2.34		$ 0.00

[1] The fourth quarter 2016 regular quarterly dividend was $0.75 per common share of which approximately $0.56 per common share was allocable to 2016 and approximately $0.19 per common share is allocable to 2017.

[2] The fourth quarter 2015 dividend of $1.90 per common share consists of a $1.25 per common share special dividend and a $0.65 per common share regular quarterly dividend. Approximately $1.35 per common share was allocable to 2015 and approximately $0.55 per common share is allocable to 2016.

[3] The fourth quarter 2014 dividend of $5.15 per common share consists of a $4.50 per common share special dividend and a $0.65 per common share regular quarterly dividend. Approximately $4.41 per common share was allocable to 2014 and approximately $0.74 per common share is allocable to 2015.