Investments Available for Sale (Details 3) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Amortized Cost
Total amortized investment	$ 1,275,972	$ 1,050,901
Fair Value
Total investments	1,276,634	1,057,613
U.S. Treasury securities
Amortized Cost
Due in 1 year	33,062
Due after 1 but within 5 years	45,040
Due after 5 but within 10 years	94,397
Due after 10 years	5,961
Subtotal	178,460
Total amortized investment	178,460	73,432
Fair Value
Due in 1 year	33,050
Due after 1 but within 5 years	44,852
Due after 5 but within 10 years	93,762
Due after 10 years	5,943
Subtotal	177,607
Total investments	177,607	74,216
U.S. agency securities
Amortized Cost
Due in 1 year	2,415
Due after 1 but within 5 years	11,540
Subtotal	13,955
Total amortized investment	13,955	4,491
Fair Value
Due in 1 year	2,420
Due after 1 but within 5 years	11,362
Subtotal	13,782
Total investments	13,782	4,520
Municipal debt securities
Amortized Cost
Due in 1 year	1,036
Due after 1 but within 5 years	83,915
Due after 5 but within 10 years	97,983
Due after 10 years	89,799
Subtotal	272,733
Total amortized investment	272,733	191,723
Fair Value
Due in 1 year	1,040
Due after 1 but within 5 years	84,497
Due after 5 but within 10 years	101,496
Due after 10 years	92,795
Subtotal	279,828
Total investments	279,828	195,546
Corporate debt securities
Amortized Cost
Due in 1 year	7,617
Due after 1 but within 5 years	276,448
Due after 5 but within 10 years	112,905
Due after 10 years	2,276
Subtotal	399,246
Total amortized investment	399,246	295,507
Fair Value
Due in 1 year	7,616
Due after 1 but within 5 years	274,633
Due after 5 but within 10 years	112,194
Due after 10 years	2,289
Subtotal	396,732
Total investments	396,732	296,829
Mortgage-backed securities
Amortized Cost
Total amortized investment	56,380	66,396
Fair Value
Total investments	55,356	66,086
Asset-backed securities
Amortized Cost
Total amortized investment	127,919	126,474
Fair Value
Total investments	126,629	126,188
Money market funds
Amortized Cost
Total amortized investment	67,098	210,688
Fair Value
Total investments	67,098	210,688
U.S. Agency \| U.S. agency mortgage-backed securities
Amortized Cost
Total amortized investment	160,181	82,190
Fair Value
Total investments	$ 159,602	$ 83,540

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
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