Investments Available for Sale (Details 3) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Amortized Cost
Amortized Cost	$ 1,549,576	$ 1,275,972
Fair Value
Total investments	1,582,156	1,276,634
U.S. Treasury securities
Amortized Cost
Due in 1 year	29,202
Due after 1 but within 5 years	32,161
Due after 5 but within 10 years	112,209
Due after 10 years	14,975
Subtotal	188,547
Amortized Cost	188,547	178,460
Fair Value
Due in 1 year	29,222
Due after 1 but within 5 years	32,490
Due after 5 but within 10 years	115,538
Due after 10 years	15,519
Subtotal	192,769
Total investments	192,769	177,607
U.S. agency securities
Amortized Cost
Due in 1 year	0
Due after 1 but within 5 years	17,319
Subtotal	17,319
Amortized Cost	17,319	13,955
Fair Value
Due in 1 year	0
Due after 1 but within 5 years	17,385
Subtotal	17,385
Total investments	17,385	13,782
Municipal debt securities
Amortized Cost
Due in 1 year	5,497
Due after 1 but within 5 years	102,729
Due after 5 but within 10 years	121,513
Due after 10 years	88,525
Subtotal	318,264
Amortized Cost	318,264	272,733
Fair Value
Due in 1 year	5,531
Due after 1 but within 5 years	103,752
Due after 5 but within 10 years	128,980
Due after 10 years	93,800
Subtotal	332,063
Total investments	332,063	279,828
Corporate debt securities
Amortized Cost
Due in 1 year	31,708
Due after 1 but within 5 years	251,267
Due after 5 but within 10 years	148,348
Due after 10 years	2,501
Subtotal	433,824
Amortized Cost	433,824	399,246
Fair Value
Due in 1 year	31,743
Due after 1 but within 5 years	254,381
Due after 5 but within 10 years	155,187
Due after 10 years	2,571
Subtotal	443,882
Total investments	443,882	396,732
Mortgage-backed securities
Amortized Cost
Amortized Cost	47,569	56,380
Fair Value
Total investments	48,465	55,356
Asset-backed securities
Amortized Cost
Amortized Cost	127,691	127,919
Fair Value
Total investments	127,498	126,629
Money market funds
Amortized Cost
Amortized Cost	135,484	67,098
Fair Value
Total investments	135,484	67,098
U.S. Agency \| Mortgage backed securities
Amortized Cost
Amortized Cost	280,878	160,181
Fair Value
Total investments	$ 284,610	$ 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

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