Subsequent Events (Details) - USD ($) $ / shares in Units, shares in Thousands																																																1 Months Ended	3 Months Ended								12 Months Ended
	Jan. 29, 2018	Jan. 27, 2018	Dec. 28, 2017	Dec. 27, 2017	Nov. 27, 2017	Oct. 27, 2017	Sep. 28, 2017	Sep. 27, 2017	Aug. 28, 2017	Jul. 27, 2017	Jun. 29, 2017	Jun. 27, 2017	May 30, 2017	Apr. 28, 2017	Apr. 27, 2017	Mar. 30, 2017	Mar. 27, 2017	Feb. 27, 2017	Jan. 30, 2017	Jan. 27, 2017	Dec. 28, 2016	Dec. 27, 2016	Nov. 29, 2016	Nov. 27, 2016	Oct. 27, 2016	Sep. 27, 2016	Aug. 29, 2016	Jul. 27, 2016	Jun. 29, 2016	May 27, 2016	Apr. 27, 2016	Mar. 28, 2016	Feb. 26, 2016	Jan. 27, 2016	Dec. 30, 2015	Dec. 28, 2015	Nov. 27, 2015	Oct. 27, 2015	Sep. 28, 2015	Aug. 27, 2015	Jul. 27, 2015	Jun. 29, 2015	May 27, 2015	Apr. 27, 2015	Mar. 27, 2015	Feb. 27, 2015	Jan. 27, 2015	Jan. 26, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Subsequent Event [Line Items]
Common stock dividends cash paid (in dollars per share)			$ 0.19		$ 0.19	$ 0.19	$ 0.19		$ 0.19	$ 0.19	$ 0.19		$ 0.19	$ 0.19		$ 0.19		$ 0.19	$ 0.19			$ 0.22	$ 0.22		$ 0.22	$ 0.22	$ 0.22	$ 0.22	$ 0.22	$ 0.22	$ 0.27	$ 0.33	$ 0.33	$ 0.33	$ 0.33		$ 0.33	$ 0.33	$ 0.33	$ 0.33	$ 0.32	$ 0.32	$ 0.32	$ 0.32	$ 0.32	$ 0.32	$ 0.32
Aggregate amount paid to holders of record (in dollars)			$ 8,046,000		$ 7,957,000	$ 7,956,000	$ 7,870,000		$ 7,839,000	$ 7,839,000	$ 6,983,000		$ 6,984,000	$ 6,984,000		$ 6,983,000		$ 6,984,000	$ 6,984,000			$ 8,086,000	$ 8,086,000		$ 8,086,000	$ 8,087,000	$ 8,087,000	$ 8,087,000	$ 8,087,000	$ 8,087,000	$ 9,925,000	$ 12,131,000	$ 12,131,000	$ 12,131,000	$ 12,859,000		$ 13,176,000	$ 13,438,000	$ 14,394,000	$ 14,477,000	$ 14,045,000	$ 14,045,000	$ 14,089,000	$ 14,133,000	$ 14,149,000	$ 14,169,000	$ 14,168,000										$ 89,409,000	$ 111,011,000	$ 167,142,000
Dividends declared per common share (in dollars per share)																																																	$ 0.57	$ 0.57	$ 0.57	$ 0.57	$ 0.66	$ 0.66	$ 0.71	$ 0.99	$ 2.28	$ 3.02	$ 3.89
Series A Preferred Stock
Subsequent Event [Line Items]
Preferred stock dividends cash paid (in dollars per share)				$ 0.17	$ 0.17	$ 0.17		$ 0.17	$ 0.17	$ 0.17		$ 0.17	$ 0.17		$ 0.17		$ 0.17	$ 0.17		$ 0.17	$ 0.17			$ 0.17	$ 0.17	$ 0.17	$ 0.17	$ 0.17	$ 0.17	$ 0.17	$ 0.17	$ 0.17	$ 0.17	$ 0.17		$ 0.17	$ 0.17	$ 0.17	$ 0.17	$ 0.17	$ 0.17	$ 0.17	$ 0.17	$ 0.17	$ 0.17	$ 0.17	$ 0.17
Aggregate amount paid to holders of record (in dollars)				$ 374,800	$ 374,800	$ 374,800		$ 374,800	$ 374,800	$ 374,800		$ 374,800	$ 374,800		$ 374,800		$ 374,800	$ 374,800		$ 374,800	$ 374,800			$ 374,800	$ 374,800	$ 374,800	$ 374,800	$ 374,800	$ 374,800	$ 374,800	$ 374,800	$ 374,800	$ 374,800	$ 374,800		$ 374,800	$ 374,800	$ 374,800	$ 374,800	$ 374,800	$ 374,800	$ 374,800	$ 374,800	$ 374,800	$ 374,800	$ 374,800	$ 374,800										$ 4,497,600	$ 4,497,600	$ 4,498,000
Series B Preferred Stock
Subsequent Event [Line Items]
Issuance of Series B Preferred stock, net of expenses																																																									14,815,000	0	0
Preferred stock dividends cash paid (in dollars per share)				$ 0.16	$ 0.16	$ 0.16		$ 0.16	$ 0.16	$ 0.16		$ 0.16	$ 0.16		$ 0.16		$ 0.16	$ 0.16		$ 0.16	$ 0.16			$ 0.16	$ 0.16	$ 0.16	$ 0.16	$ 0.16	$ 0.16	$ 0.16	$ 0.16	$ 0.16	$ 0.16	$ 0.16		$ 0.16	$ 0.16	$ 0.16	$ 0.16	$ 0.16	$ 0.16	$ 0.16	$ 0.16	$ 0.16	$ 0.16	$ 0.16	$ 0.16
Aggregate amount paid to holders of record (in dollars)				$ 1,019,000	$ 998,000	$ 987,000		$ 962,000	$ 927,000	$ 927,000		$ 927,000	$ 927,000		$ 927,000		$ 927,000	$ 927,000		$ 927,000	$ 927,000			$ 927,000	$ 927,000	$ 927,000	$ 927,000	$ 927,000	$ 927,000	$ 927,000	$ 927,000	$ 927,000	$ 927,000	$ 927,000		$ 927,000	$ 927,000	$ 927,000	$ 927,000	$ 927,000	$ 927,000	$ 927,000	$ 927,000	$ 927,000	$ 927,000	$ 927,000	$ 927,000										$ 11,382,000	$ 11,124,000	$ 11,124,000
Subsequent Event
Subsequent Event [Line Items]
Common stock dividends cash paid (in dollars per share)	$ 0.19
Aggregate amount paid to holders of record (in dollars)	$ 8,046,000
Dividends declared per common share (in dollars per share)	$ 0.19
Subsequent Event | Series A Preferred Stock
Subsequent Event [Line Items]
Preferred stock dividends cash paid (in dollars per share)		$ 0.17
Aggregate amount paid to holders of record (in dollars)		$ 375,000
Rate per preferred share dividends declared (in dollars per share)		$ 0.17
Subsequent Event | Series B Preferred Stock
Subsequent Event [Line Items]
Issuance of Series B Preferred stock, net (in shares)																																																107
Issuance of Series B Preferred stock, net of expenses																																																$ 2,632,000
Preferred stock dividends cash paid (in dollars per share)		$ 0.16
Aggregate amount paid to holders of record (in dollars)		$ 1,039,000
Rate per preferred share dividends declared (in dollars per share)		$ 0.16