Investments (Valuation Allowance Rollforward by Portfolio Segment) (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2017	Mar. 31, 2016
Mortgage Loans on Real Estate [Line Items]
Balance, beginning of period	$ 1,775	$ 640
Provision (release)	(3)	80
Balance, end of period	1,772	720
Commercial
Mortgage Loans on Real Estate [Line Items]
Balance, beginning of period	1,419	578
Provision (release)	(21)	80
Balance, end of period	1,398	658
Agricultural
Mortgage Loans on Real Estate [Line Items]
Balance, beginning of period	356	62
Provision (release)	18	0
Balance, end of period	$ 374	$ 62

Amount of expense related to estimated loss from loan and lease transactions.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 225
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04.11)
-URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3602-108585

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=66008989&loc=SL6953423-111524

Name:	us-gaap_ProvisionForLoanAndLeaseLosses
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration