Other Liabilities (Senior Notes) (Details) - Senior Notes - USD ($)		6 Months Ended
Apr. 11, 2012	Jun. 30, 2018
Debt Instrument [Line Items]
Proceeds from issuance of debt	$ 100,000,000.0
Proceed from senior notes net of offering expenses and underwriting discount	$ 96,600,000
Stated interest rate		8.00%
Effective interest rate		8.31%
Redemption price as percentage of principal amount		100.00%

Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

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Percentage price of original principal amount of debt at which debt can be redeemed by the issuer.

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