Investments Available for Sale (Details 3) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Amortized Cost
Total amortized investment	$ 1,348,767	$ 1,275,972
Fair Value
Total investments	1,368,502	1,276,634
U.S. Treasury securities
Amortized Cost
Due in 1 year	38,647
Due after 1 but within 5 years	66,474
Due after 5 but within 10 years	88,230
Due after 10 years	15,111
Subtotal	208,462
Total amortized investment	208,462	178,460
Fair Value
Due in 1 year	38,656
Due after 1 but within 5 years	67,147
Due after 5 but within 10 years	90,652
Due after 10 years	15,325
Subtotal	211,780
Total investments	211,780	177,607
U.S. agency securities
Amortized Cost
Due in 1 year	2,408
Due after 1 but within 5 years	12,140
Subtotal	14,548
Total amortized investment	14,548	13,955
Fair Value
Due in 1 year	2,413
Due after 1 but within 5 years	12,244
Subtotal	14,657
Total investments	14,657	13,782
Municipal debt securities
Amortized Cost
Due in 1 year	2,043
Due after 1 but within 5 years	86,093
Due after 5 but within 10 years	106,907
Due after 10 years	98,405
Subtotal	293,448
Total amortized investment	293,448	272,733
Fair Value
Due in 1 year	2,044
Due after 1 but within 5 years	87,061
Due after 5 but within 10 years	112,055
Due after 10 years	102,951
Subtotal	304,111
Total investments	304,111	279,828
Corporate debt securities
Amortized Cost
Due in 1 year	20,135
Due after 1 but within 5 years	265,999
Due after 5 but within 10 years	124,875
Due after 10 years	518
Subtotal	411,527
Total amortized investment	411,527	399,246
Fair Value
Due in 1 year	20,124
Due after 1 but within 5 years	267,539
Due after 5 but within 10 years	128,491
Due after 10 years	534
Subtotal	416,688
Total investments	416,688	396,732
Mortgage-backed securities
Amortized Cost
Total amortized investment	53,171	56,380
Fair Value
Total investments	53,046	55,356
Asset-backed securities
Amortized Cost
Total amortized investment	123,123	127,919
Fair Value
Total investments	121,729	126,629
Money market funds
Amortized Cost
Total amortized investment	68,488	67,098
Fair Value
Total investments	68,488	67,098
U.S. Agency \| Mortgage backed securities
Amortized Cost
Total amortized investment	176,000	160,181
Fair Value
Total investments	$ 178,003	$ 159,602

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 25
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=28360136&loc=d3e22054-111558

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