Stockholders' Equity - Additional Information (Details)																																																				1 Months Ended			2 Months Ended	4 Months Ended		6 Months Ended	7 Months Ended		12 Months Ended			22 Months Ended
	Feb. 27, 2020 $ / shares	Jan. 29, 2020 shares	Jan. 28, 2020 USD ($) $ / shares shares	Jan. 27, 2020 USD ($) $ / shares	Jan. 24, 2020 $ / shares shares	Jan. 23, 2020 $ / shares shares	Dec. 27, 2019 USD ($) $ / shares	Nov. 27, 2019 USD ($) $ / shares	Oct. 28, 2019 USD ($) $ / shares	Sep. 27, 2019 USD ($) $ / shares	Aug. 27, 2019 USD ($) $ / shares	Jul. 29, 2019 USD ($) $ / shares	Jun. 27, 2019 USD ($) $ / shares	Jun. 25, 2019 shares	Jun. 24, 2019 $ / shares shares	Jun. 19, 2019 USD ($) $ / shares shares	Jun. 04, 2019 shares	May 28, 2019 USD ($) $ / shares	Apr. 29, 2019 USD ($) $ / shares	Mar. 27, 2019 USD ($) $ / shares	Feb. 27, 2019 USD ($) $ / shares	Feb. 27, 2019 USD ($) $ / shares	Jan. 28, 2019 USD ($) $ / shares	Jan. 17, 2019 USD ($) $ / shares	Jan. 11, 2019 USD ($) $ / shares	Dec. 27, 2018 USD ($) $ / shares	Dec. 19, 2018 USD ($) $ / shares	Nov. 27, 2018 USD ($) $ / shares	Oct. 29, 2018 USD ($) $ / shares	Sep. 27, 2018 USD ($) $ / shares	Aug. 27, 2018 USD ($) $ / shares	Jul. 27, 2018 USD ($) $ / shares	Jun. 27, 2018 USD ($) $ / shares	May 29, 2018 USD ($) $ / shares	Apr. 27, 2018 USD ($) $ / shares	Mar. 27, 2018 USD ($) $ / shares	Feb. 27, 2018 USD ($) $ / shares	Jan. 29, 2018 USD ($) $ / shares	Dec. 27, 2017 USD ($) $ / shares	Nov. 27, 2017 USD ($) $ / shares	Oct. 27, 2017 USD ($) $ / shares	Sep. 27, 2017 USD ($) $ / shares	Aug. 28, 2017 USD ($) $ / shares	Jul. 27, 2017 USD ($) $ / shares	Jun. 30, 2017 USD ($) $ / shares	Jun. 27, 2017 USD ($) $ / shares	May 30, 2017 USD ($) $ / shares	Apr. 27, 2017 USD ($) $ / shares	Mar. 27, 2017 USD ($) $ / shares	Feb. 27, 2017 USD ($) $ / shares	Jan. 27, 2017 USD ($) $ / shares	Feb. 14, 2020 USD ($)	Jan. 26, 2018 USD ($) $ / shares shares	Oct. 06, 2017 USD ($) $ / shares shares	Jun. 03, 2019 shares	Dec. 10, 2018 USD ($) $ / shares shares	Dec. 30, 2017 USD ($) $ / shares shares	Dec. 31, 2019 USD ($) $ / shares shares	Dec. 31, 2019 USD ($) $ / shares shares	Dec. 31, 2019 USD ($) $ / shares shares	Dec. 31, 2019 USD ($) director $ / shares shares	Dec. 31, 2018 USD ($) $ / shares shares	Dec. 31, 2017 USD ($) shares	Jun. 20, 2019 USD ($) shares	Feb. 15, 2019 $ / shares shares	Oct. 02, 2017 $ / shares shares	Aug. 30, 2017 shares
Class of Stock [Line Items]
Preferred stock, par value (in dollars per share) | $ / shares															$ 0.001																																											$ 0.001	$ 0.001	$ 0.001	$ 0.001	$ 0.001
Preferred stock, shares authorized (in shares)																																																										50,000,000	50,000,000	50,000,000	50,000,000	50,000,000
Shares authorized, increase (decrease) (in shares)															10,320,000
Preferred stock, undesignated shares authorized (in shares)																																																										32,030,000	32,030,000	32,030,000	32,030,000
Common stock, shares authorized (in shares)																																																										125,000,000	125,000,000	125,000,000	125,000,000	125,000,000
Common stock, par value (in dollars per share) | $ / shares																																																										$ 0.001	$ 0.001	$ 0.001	$ 0.001	$ 0.001
Common stock, shares issued (in shares)																																																										58,877,000	58,877,000	58,877,000	58,877,000	43,702,000
Common stock, shares outstanding (in shares)																																																										58,876,984	58,876,984	58,876,984	58,876,984	43,702,000
Proceeds from issuance of common stock | $																																																													$ 49,795,000	$ 2,632,000
Remaining shares authorized to be repurchased (in shares)																																																										8,250,000	8,250,000	8,250,000	8,250,000	1,874,000	1,874,343
Shares authorized, increase (decrease) (in shares)																	9,000,000
Common stock repurchased (in shares)																																																							250,000				750,000
At-The-Market Offering Program
Class of Stock [Line Items]
Common stock, shares authorized (in shares)																																																																	7,000	5,000
Common stock, par value (in dollars per share) | $ / shares																																																																	$ 0.001	$ 0.001
Sale of stock, commission rate																																																																	2.00%
Series A Preferred Stock
Class of Stock [Line Items]
Preferred stock, called for redemption (in shares)														2,181,000
Preferred stock, dividend rate																																																													8.25%	8.25%
Preferred stock, liquidation preference per share (in dollars per share) | $ / shares																																																														$ 25.00
Preferred stock, aggregate liquidation preference | $																																																														$ 54,514,000
Payments of dividends | $												$ 375,000	$ 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										$ 2,249,000	$ 4,498,000	$ 4,498,000
Preferred stock, shares issued (in shares)																																																														2,181,000
Preferred stock, par value (in dollars per share) | $ / shares																																																														$ 0.001
Preferred stock, designated but unissued shares authorized (in shares)																																																														7,429,000
Preferred stock dividends cash paid (in dollars per share) | $ / shares													$ 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
Preferred stock, shares outstanding (in shares)																																																										2,180,572	2,180,572	2,180,572	2,180,572	2,180,572
Series B Preferred Stock
Class of Stock [Line Items]
Preferred stock, dividend rate																																																													7.875%	7.875%
Preferred stock, liquidation preference per share (in dollars per share) | $ / shares																																																										$ 25.00	$ 25.00	$ 25.00	$ 25.00	$ 25
Preferred stock, aggregate liquidation preference | $																																																										$ 209,584,000	$ 209,584,000	$ 209,584,000	$ 209,584,000	$ 159,232,000
Payments of dividends | $							$ 1,291,000	$ 1,210,000	$ 1,190,000	$ 1,168,000	$ 1,142,000	$ 1,100,000	$ 1,059,000					$ 1,045,000	$ 1,045,000	$ 1,045,000		$ 1,045,000	$ 1,045,000			$ 1,045,000		$ 1,045,000	$ 1,045,000	$ 1,045,000	$ 1,045,000	$ 1,045,000	$ 1,045,000	$ 1,045,000	$ 1,045,000	$ 1,045,000	$ 1,045,000	$ 1,039,000	$ 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										$ 13,385,000	$ 12,534,000	11,382,000
Preferred stock, shares issued (in shares)																																																										8,383,000	8,383,000	8,383,000	8,383,000	6,369,000
Preferred stock, par value (in dollars per share) | $ / shares																																																										$ 0.001	$ 0.001	$ 0.001	$ 0.001	$ 0.001
Preferred stock, designated but unissued shares authorized (in shares)																																																										9,587,000	9,587,000	9,587,000	9,587,000
Preferred stock, shares authorized (in shares)																																																										17,970,000	17,970,000	17,970,000	17,970,000
Preferred stock dividends cash paid (in dollars per share) | $ / shares							$ 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
Preferred stock, period stock receives voting rights if dividends are not paid (in months)																																																													18 months
Number of additional directors elected | director																																																													2
Preferred stock issued (in shares)																100,000																																					107,000	619,000		840,000	612,000	1,914,000
Preferred stock, shares outstanding (in shares)																																																										8,383,000	8,383,000	8,383,000	8,383,000	6,369,000
Proceeds from issuance of preferred stock, net | $																$ 2,489,000																																					$ 2,632,000	$ 16,500,000		$ 19,001,000	$ 14,968,000	$ 47,306,000			$ 44,289,000	$ 2,632,000	14,815,000
Per Share price (in dollars per share) | $ / shares																$ 24.81																																					$ 24.62	$ 26.44		$ 22.61	$ 24.44	$ 24.74	$ 24.74	$ 24.74	$ 24.74
Proceeds from issuance of common stock | $																																																															$ 14,968,000
Series B Preferred Stock | August 30, 2017, Preferred B ATM Sales Agreement
Class of Stock [Line Items]
Preferred stock, shares authorized (in shares)																																																																			2,000
Preferred stock issued (in shares)																																																													884,000			100,000
Payments of stock issuance costs | $																																																													$ 263,000			$ 25,000
Proceeds from issuance of preferred stock, net | $																																																																$ 2,489,000
Series B Preferred Stock | June 24, 2019, Preferred B ATM Sales Agreement
Class of Stock [Line Items]
Preferred stock, shares authorized (in shares)															9,000,000
Preferred stock issued (in shares)																																																													1,914,000
Payments of stock issuance costs | $																																																													$ 689,000
Proceeds from issuance of preferred stock, net | $																																																													$ 47,306,000
Series B Preferred Stock | Dividend Reinvestment Program
Class of Stock [Line Items]
Preferred stock, shares authorized (in shares)															2,500,000
Preferred stock issued (in shares)																																																													16
Series B Preferred Stock | Scenario, Forecast
Class of Stock [Line Items]
Preferred stock dividends cash paid (in dollars per share) | $ / shares	$ 0.16
Series B Preferred Stock | Subsequent Event
Class of Stock [Line Items]
Preferred stock, called for redemption (in shares)					8,383,000
Preferred stock, liquidation preference per share (in dollars per share) | $ / shares					$ 25.00
Payments of dividends | $				$ 1,375,000
Preferred stock dividends cash paid (in dollars per share) | $ / shares				$ 0.16
Percent of outstanding shares intended to be redeemed		100.00%
Series B Preferred Stock | Subsequent Event | Scenario, Forecast
Class of Stock [Line Items]
Preferred stock dividends cash paid (in dollars per share) | $ / shares	0.16
Series C Preferred Stock | Subsequent Event
Class of Stock [Line Items]
Preferred stock, dividend rate			7.00%
Preferred stock, par value (in dollars per share) | $ / shares			$ 0.001
Preferred stock, shares authorized (in shares)			10,000,000
Payments of stock issuance costs | $																																																				$ 327,000
Proceeds from issuance of preferred stock, net | $																																																				$ 29,853,000
Series C Preferred Stock | Subsequent Event | January 23, 2020 Underwriting Agreement
Class of Stock [Line Items]
Preferred stock, dividend rate						7.00%
Preferred stock, liquidation preference per share (in dollars per share) | $ / shares						$ 25.00
Preferred stock, par value (in dollars per share) | $ / shares						$ 0.001
Preferred stock, shares authorized (in shares)						3,000,000
Per Share price (in dollars per share) | $ / shares						$ 25.00
Consideration received on transaction | $			$ 86,250,000
Series C Preferred Stock | Subsequent Event | January 29, 2020, Equity Sales Agreement
Class of Stock [Line Items]
Preferred stock, shares authorized (in shares)		6,550,000
Series C Preferred Stock | Subsequent Event | Over-Allotment Option
Class of Stock [Line Items]
Preferred stock, shares authorized (in shares)						450,000
Over-allotment option term						30 days
Series C Preferred Stock | Subsequent Event | Scenario, Forecast
Class of Stock [Line Items]
Preferred stock dividends cash paid (in dollars per share) | $ / shares	$ 0.15
Common Stock
Class of Stock [Line Items]
Per Share price (in dollars per share) | $ / shares																					$ 19.98	$ 19.98		$ 20.00	$ 20.98		$ 21.53																		$ 25.96													$ 17.77	$ 17.77	$ 17.77	$ 17.77
Proceeds from issuance of common stock | $																					$ 165,374,000			$ 137,946,000	$ 18,540,000		$ 19,013,000																		$ 116,693,000
Common stock repurchased (in shares)																																																												1,000,000