Investments (Mortgage Loans by Credit Quality Indicator) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	$ 4,983,354	$ 4,413,171
Loans Receivable, Gross, Commercial, Construction	$ 32,620	$ 9,686
Mortgage Loans On Real Estate Commercial And Consumer Net Percentage Of Total	100.00%	100.00%
Greater than 1.20x
Financing Receivable, Recorded Investment [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	$ 4,561,177	$ 4,182,753
1.00x - 1.20x
Financing Receivable, Recorded Investment [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	233,260	151,281
Less than 1.00x
Financing Receivable, Recorded Investment [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	156,297	69,451
0% - 59.99%
Financing Receivable, Recorded Investment [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	2,523,670	2,206,208
Loans Receivable, Gross, Commercial, Construction	$ 13,691	$ 0
Mortgage Loans On Real Estate Commercial And Consumer Net Percentage Of Total	50.60%	50.00%
0% - 59.99% \| Greater than 1.20x
Financing Receivable, Recorded Investment [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	$ 2,410,556	$ 2,148,428
0% - 59.99% \| 1.00x - 1.20x
Financing Receivable, Recorded Investment [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	61,246	53,979
0% - 59.99% \| Less than 1.00x
Financing Receivable, Recorded Investment [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	38,177	3,801
60% - 69.99%
Financing Receivable, Recorded Investment [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	1,749,331	1,608,078
Loans Receivable, Gross, Commercial, Construction	$ 18,929	$ 0
Mortgage Loans On Real Estate Commercial And Consumer Net Percentage Of Total	35.10%	36.40%
60% - 69.99% \| Greater than 1.20x
Financing Receivable, Recorded Investment [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	$ 1,618,374	$ 1,517,029
60% - 69.99% \| 1.00x - 1.20x
Financing Receivable, Recorded Investment [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	73,908	47,128
60% - 69.99% \| Less than 1.00x
Financing Receivable, Recorded Investment [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	38,120	43,921
70% - 79.99%
Financing Receivable, Recorded Investment [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	517,147	431,274
Loans Receivable, Gross, Commercial, Construction	$ 0	$ 0
Mortgage Loans On Real Estate Commercial And Consumer Net Percentage Of Total	10.40%	9.80%
70% - 79.99% \| Greater than 1.20x
Financing Receivable, Recorded Investment [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	$ 414,269	$ 396,446
70% - 79.99% \| 1.00x - 1.20x
Financing Receivable, Recorded Investment [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	48,438	19,461
70% - 79.99% \| Less than 1.00x
Financing Receivable, Recorded Investment [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	54,440	15,367
Greater than 80%
Financing Receivable, Recorded Investment [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	193,206	167,611
Loans Receivable, Gross, Commercial, Construction	$ 0	$ 9,686
Mortgage Loans On Real Estate Commercial And Consumer Net Percentage Of Total	3.90%	3.80%
Greater than 80% \| Greater than 1.20x
Financing Receivable, Recorded Investment [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	$ 117,978	$ 120,850
Greater than 80% \| 1.00x - 1.20x
Financing Receivable, Recorded Investment [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	49,668	30,713
Greater than 80% \| Less than 1.00x
Financing Receivable, Recorded Investment [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	$ 25,560	$ 6,362

The amount represents the total percentage of each property type in comparison to the total of mortgage loans whose balance represents the amount of loans that are secured by real estate mortgages, offset by the reserve to cover probable credit losses on the loan portfolio.

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Amount before allowance of commercial construction loans. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes loans covered under loss sharing agreements.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
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Amount before allowance of commercial loans issued to businesses to acquire, develop, construct, improve, or refinance land or building. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes loans covered under loss sharing agreements.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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