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Investment Agreement, Number Of Shares Issued In Transaction

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Preferred Stock, Liquidation Preference Per Share, Per Annum

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Preferred Stock, Liquidation Preference Per Share, Quarterly

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Preferred Stock, Percentage Interest In Underlying Shares

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Preferred Stock, Right To Elect Directors, Number Of Directors

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Preferred Stock, Right To Elect Directors, Required Number Of Dividend Periods In Arrears

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The maximum number of common shares and nonredeemable preferred shares (or preferred stock redeemable solely at the option of the issuer) permitted to be issued by an entity's charter and bylaws.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Aggregate dividends paid during the period for each share of common stock outstanding.

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Aggregate dividends declared during the period for each share of common stock outstanding.

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The maximum number of common shares permitted to be issued by an entity's charter and bylaws.

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Amount of paid and unpaid common stock dividends declared with the form of settlement in cash, stock and payment-in-kind (PIK).

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Amount of paid and unpaid preferred stock dividends declared with the form of settlement in cash, stock and payment-in-kind (PIK).

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The percentage rate used to calculate dividend payments on preferred stock.

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The per share liquidation preference (or restrictions) of nonredeemable preferred stock (or preferred stock redeemable solely at the option of the issuer) that has a preference in involuntary liquidation considerably in excess of the par or stated value of the shares. The liquidation preference is the difference between the preference in liquidation and the par or stated values of the share.

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Face amount or stated value per share of preferred stock nonredeemable or redeemable solely at the option of the issuer.

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The redemption (or callable) amount of currently redeemable preferred stock. Includes amounts representing dividends not currently declared or paid but which will be payable under the redemption features or for which ultimate payment is solely within the control of the issuer.

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The price per share at which the preferred stock of an entity that has priority over common stock in the distribution of dividends and in the event of liquidation of the entity is redeemed or may be called at. The redemption features of this preferred stock are solely within the control of the issuer.

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The maximum number of nonredeemable preferred shares (or preferred stock redeemable solely at the option of the issuer) permitted to be issued by an entity's charter and bylaws.

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Total number of nonredeemable preferred shares (or preferred stock redeemable solely at the option of the issuer) issued to shareholders (includes related preferred shares that were issued, repurchased, and remain in the treasury). May be all or portion of the number of preferred shares authorized. Excludes preferred shares that are classified as debt.

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Aggregate share number for all nonredeemable preferred stock (or preferred stock redeemable solely at the option of the issuer) held by stockholders. Does not include preferred shares that have been repurchased.

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The cash inflow from issuance of preferred stocks identified as being convertible into another form of financial instrument, typically the entity's common stock.

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Proceeds from issuance of capital stock which provides for a specific dividend that is paid to the shareholders before any dividends to common stockholders and which takes precedence over common stockholders in the event of liquidation.

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Number of new stock issued during the period.

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Number of stock bought back by the entity at the exercise price or redemption price.

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Amount of stock repurchase plan authorized.

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Amount remaining of a stock repurchase plan authorized.

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Shareholders' Equity (Narrative) (Details)												1 Months Ended			3 Months Ended								12 Months Ended
Shareholders' Equity (Narrative) (Details)	Dec. 31, 2018 USD ($) director period $ / shares shares	Dec. 20, 2018 shares	Dec. 14, 2018 $ / shares	Oct. 30, 2018 USD ($)	Sep. 28, 2018 $ / shares	Sep. 14, 2018 $ / shares	Jun. 29, 2018 $ / shares	Jun. 15, 2018 $ / shares	Mar. 29, 2018 $ / shares	Mar. 15, 2018 $ / shares	Jun. 27, 2013 USD ($) shares	Jun. 30, 2018 USD ($) $ / shares shares	May 31, 2013 USD ($) $ / shares shares	Mar. 31, 2004 USD ($) $ / shares shares	Dec. 31, 2018 USD ($) director period $ / shares shares	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($) $ / shares shares	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($) $ / shares shares	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2018 USD ($) director period $ / shares shares	Dec. 31, 2017 USD ($) $ / shares shares	Dec. 31, 2016 USD ($) shares	Dec. 31, 2013 USD ($)	Nov. 10, 2017 USD ($)
Class of Stock [Line Items]
Aggregate authorized shares (in shares) \| shares	325,000,000														325,000,000								325,000,000
Authorized common shares (in shares) \| shares	225,000,000														225,000,000								225,000,000
Authorized preference shares (in shares) \| shares	100,000,000														100,000,000								100,000,000
Dividends on preference shares \| $															$ 9,189,000	$ 9,708,000	$ 5,596,000	$ 5,595,000	$ 5,595,000	$ 5,595,000	$ 5,596,000	$ 5,595,000	$ 30,088,000	$ 22,381,000	$ 22,381,000
Preference shares, issued, value \| $																							$ 241,448,000	$ 0
Par value (in usd per share)	$ 1														$ 1				$ 1				$ 1	$ 1
Preference shares, shares outstanding (in shares) \| shares	16,010,000														16,010,000				16,000,000				16,010,000	16,000,000
Shares issued (in shares) \| shares	16,010,000														16,010,000				16,000,000				16,010,000	16,000,000
Common shares
Class of Stock [Line Items]
Preference shares, shares issued (in shares) \| shares																							1,947,000	0	0
Common shares \| Private Placement \| State Farm
Class of Stock [Line Items]
Investment Agreement, shares issued in transaction (in shares) \| shares		1,947,496
Investment Agreement, consideration received per transaction \| $				$ 250,000,000
Retained earnings
Class of Stock [Line Items]
Dividends on preference shares \| $																							$ 30,088,000	$ 22,381,000	$ 22,381,000
Dividends on common shares \| $																							(52,841,000)	$ (51,370,000)	$ (51,583,000)
Common shares
Class of Stock [Line Items]
Dividends declared per common share (in usd per share)			$ 0.33			$ 0.33		$ 0.33		$ 0.33
Dividends paid per common share (in usd per share)	$ 0.33				$ 0.33		$ 0.33		$ 0.33
Share repurchase program, authorized aggregate amount \| $																											$ 500,000,000
Share repurchase program, remaining authorized shares (in shares) \| $	$ 500,000,000														$ 500,000,000								$ 500,000,000
Series C Preferred Stock
Class of Stock [Line Items]
Dividend rate, percentage																							6.08%
Liquidation preference per annum (in usd per share)	$ 1.52														$ 1.52								$ 1.52
Quarterly liquidation preference (in usd per share)	$ 0.38														$ 0.38								$ 0.38
Preference shares, issued, value \| $														$ 250,000,000
Preference shares, shares issued (in shares) \| shares														10,000,000
Par value (in usd per share)														$ 25
Preference shares, shares redeemed (in shares) \| shares											5,000,000
Preference shares, redemption amount \| $											$ 125,000,000
Preference shares, shares outstanding (in shares) \| shares											5,000,000
Proceeds from Issuance of Convertible Preferred Stock \| $												$ 250,000,000
Right to elect directors, required number of dividend periods in arrears \| period	6														6								6
Right to elect directors, number of directors \| director	2														2								2
Series E Preferred Stock
Class of Stock [Line Items]
Dividend rate, percentage																							5.375%
Liquidation preference per annum (in usd per share)	$ 1.34375														$ 1.34375								$ 1.34375
Quarterly liquidation preference (in usd per share)	0.3359375														0.3359375								0.3359375
Preference shares, issued, value \| $													$ 275,000,000													$ 0
Preference shares, shares issued (in shares) \| shares													11,000,000
Par value (in usd per share)													$ 25
Redemption price per share (in usd per share)	$ 25														$ 25								$ 25
Series F Preferred Stock
Class of Stock [Line Items]
Dividend rate, percentage												5.75%
Liquidation preference per annum (in usd per share)												$ 1,437.50					$ 1,437.50
Quarterly liquidation preference (in usd per share)												$ 359.375					$ 359.375
Shares issued (in shares) \| shares												10,000					10,000
Liquidation preference (in usd per share)												$ 25,000					$ 25,000
Redemption price per share (in usd per share)												25,000					25,000
Depositary Shares
Class of Stock [Line Items]
Liquidation preference per annum (in usd per share)												1.4375					1.4375
Quarterly liquidation preference (in usd per share)												$ 0.359375					$ 0.359375
Shares issued (in shares) \| shares												10,000,000					10,000,000
Percentage interest in underlying shares												0.10%					0.10%
Redemption price per share (in usd per share)												$ 25					$ 25