Investments Available for Sale (Details 3) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Amortized Cost
Total amortized investment	$ 1,399,689	$ 1,275,972
Fair Value
Total investments	1,435,174	1,276,634
U.S. Treasury securities
Amortized Cost
Due in 1 year	36,949
Due after 1 but within 5 years	53,037
Due after 5 but within 10 years	90,728
Due after 10 years	15,043
Subtotal	195,757
Total amortized investment	195,757	178,460
Fair Value
Due in 1 year	36,972
Due after 1 but within 5 years	53,937
Due after 5 but within 10 years	95,127
Due after 10 years	15,766
Subtotal	201,802
Total investments	201,802	177,607
U.S. agency securities
Amortized Cost
Due in 1 year	2,003
Due after 1 but within 5 years	12,137
Subtotal	14,140
Total amortized investment	14,140	13,955
Fair Value
Due in 1 year	2,004
Due after 1 but within 5 years	12,335
Subtotal	14,339
Total investments	14,339	13,782
Municipal debt securities
Amortized Cost
Due in 1 year	2,255
Due after 1 but within 5 years	98,424
Due after 5 but within 10 years	122,002
Due after 10 years	91,166
Subtotal	313,847
Total amortized investment	313,847	272,733
Fair Value
Due in 1 year	2,259
Due after 1 but within 5 years	99,833
Due after 5 but within 10 years	129,935
Due after 10 years	98,176
Subtotal	330,203
Total investments	330,203	279,828
Corporate debt securities
Amortized Cost
Due in 1 year	22,643
Due after 1 but within 5 years	220,016
Due after 5 but within 10 years	135,044
Due after 10 years	3,179
Subtotal	380,882
Total amortized investment	380,882	399,246
Fair Value
Due in 1 year	22,692
Due after 1 but within 5 years	222,916
Due after 5 but within 10 years	141,568
Due after 10 years	3,249
Subtotal	390,425
Total investments	390,425	396,732
Mortgage-backed securities
Amortized Cost
Total amortized investment	50,005	56,380
Fair Value
Total investments	50,604	55,356
Asset-backed securities
Amortized Cost
Total amortized investment	129,995	127,919
Fair Value
Total investments	129,312	126,629
Money market funds
Amortized Cost
Total amortized investment	114,235	67,098
Fair Value
Total investments	114,235	67,098
U.S. Agency \| Mortgage backed securities
Amortized Cost
Total amortized investment	200,828	160,181
Fair Value
Total investments	$ 204,254	$ 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=65884222&loc=d3e22054-111558

Reference 2: http://www.xbrl.org/2003/role/presentationRef
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