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Fair Value Measurement (Quantitative Information Regarding Level 3 Valuations) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Assets:
Total assets at fair value	$ 3,395,111	$ 3,752,976
Fair Value, Inputs, Level 3 [Member] | State and municipal bonds [Member]
Assets:
Total assets at fair value	$ 0	5,000
Fair Value, Inputs, Level 3 [Member] | State and municipal bonds [Member] | Market Approach Valuation Technique [Member] | Minimum [Member]
Assets:
Comparability Adjustment	0.00%
Fair Value, Inputs, Level 3 [Member] | State and municipal bonds [Member] | Market Approach Valuation Technique [Member] | Maximum [Member]
Assets:
Comparability Adjustment	10.00%
Fair Value, Inputs, Level 3 [Member] | State and municipal bonds [Member] | Market Approach Valuation Technique [Member] | Weighted Average [Member]
Assets:
Comparability Adjustment	5.00%
Fair Value, Inputs, Level 3 [Member] | State and municipal bonds [Member] | Income Approach Valuation Technique [Member] | Minimum [Member]
Assets:
Comparability Adjustment	0.00%
Fair Value, Inputs, Level 3 [Member] | State and municipal bonds [Member] | Income Approach Valuation Technique [Member] | Maximum [Member]
Assets:
Comparability Adjustment	10.00%
Fair Value, Inputs, Level 3 [Member] | State and municipal bonds [Member] | Income Approach Valuation Technique [Member] | Weighted Average [Member]
Assets:
Comparability Adjustment	5.00%
Fair Value, Inputs, Level 3 [Member] | Corporate debt, limited observable inputs [Member]
Assets:
Total assets at fair value	$ 14,500	13,100
Fair Value, Inputs, Level 3 [Member] | Corporate debt, limited observable inputs [Member] | Market Approach Valuation Technique [Member] | Minimum [Member]
Assets:
Comparability Adjustment	0.00%
Fair Value, Inputs, Level 3 [Member] | Corporate debt, limited observable inputs [Member] | Market Approach Valuation Technique [Member] | Maximum [Member]
Assets:
Comparability Adjustment	5.00%
Fair Value, Inputs, Level 3 [Member] | Corporate debt, limited observable inputs [Member] | Market Approach Valuation Technique [Member] | Weighted Average [Member]
Assets:
Comparability Adjustment	2.50%
Fair Value, Inputs, Level 3 [Member] | Corporate debt, limited observable inputs [Member] | Income Approach Valuation Technique [Member] | Minimum [Member]
Assets:
Comparability Adjustment	0.00%
Fair Value, Inputs, Level 3 [Member] | Corporate debt, limited observable inputs [Member] | Income Approach Valuation Technique [Member] | Maximum [Member]
Assets:
Comparability Adjustment	5.00%
Fair Value, Inputs, Level 3 [Member] | Corporate debt, limited observable inputs [Member] | Income Approach Valuation Technique [Member] | Weighted Average [Member]
Assets:
Comparability Adjustment	2.50%
Fair Value, Inputs, Level 3 [Member] | Asset-backed Securities, Securitized Loans and Receivables [Member]
Assets:
Total assets at fair value	$ 800	$ 4,800
Fair Value, Inputs, Level 3 [Member] | Asset-backed Securities, Securitized Loans and Receivables [Member] | Market Approach Valuation Technique [Member] | Minimum [Member]
Assets:
Comparability Adjustment	0.00%
Fair Value, Inputs, Level 3 [Member] | Asset-backed Securities, Securitized Loans and Receivables [Member] | Market Approach Valuation Technique [Member] | Maximum [Member]
Assets:
Comparability Adjustment	5.00%
Fair Value, Inputs, Level 3 [Member] | Asset-backed Securities, Securitized Loans and Receivables [Member] | Market Approach Valuation Technique [Member] | Weighted Average [Member]
Assets:
Comparability Adjustment	2.50%
Fair Value, Inputs, Level 3 [Member] | Asset-backed Securities, Securitized Loans and Receivables [Member] | Income Approach Valuation Technique [Member] | Minimum [Member]
Assets:
Comparability Adjustment	0.00%
Fair Value, Inputs, Level 3 [Member] | Asset-backed Securities, Securitized Loans and Receivables [Member] | Income Approach Valuation Technique [Member] | Maximum [Member]
Assets:
Comparability Adjustment	5.00%
Fair Value, Inputs, Level 3 [Member] | Asset-backed Securities, Securitized Loans and Receivables [Member] | Income Approach Valuation Technique [Member] | Weighted Average [Member]
Assets:
Comparability Adjustment	2.50%

X

- Definition

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258

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- Definition

Percentage of adjustment to the observed price for a similar asset or liability when an identical transaction does not exist, used as an input to measure fair value.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (bbb)
-URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258

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