Fair Value of Financial Instruments (Tables)

9 Months Ended

Sep. 30, 2018

Schedule of assets and liabilities measured at fair vale on a recurring basis

All assets measured at fair value are categorized in the table below based upon the lowest level of significant input to the valuations. All fair value measurements at the reporting date were on a recurring basis.



September 30, 2018 (In thousands)	Quoted Prices in Active Markets for Identical Instruments (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)		Total
Recurring fair value measurements
Financial Assets:
U.S. Treasury securities	$	265,233	$	—	$	—	$	265,233
U.S. agency securities	—		32,677		—		32,677
U.S. agency mortgage-backed securities	—		566,626		—		566,626
Municipal debt securities	—		457,506		—		457,506
Non-U.S. government securities	—		44,798		—		44,798
Corporate debt securities	—		706,330		—		706,330
Residential and commercial mortgage securities	—		101,649		—		101,649
Asset-backed securities	—		299,021		—		299,021
Money market funds	191,912		—		—		191,912
Total assets at fair value	$	457,145	$	2,208,607	$	—	$	2,665,752



December 31, 2017 (In thousands)	Quoted Prices in Active Markets for Identical Instruments (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)		Total
Recurring fair value measurements
Financial Assets:
U.S. Treasury securities	$	227,805	$	—	$	—	$	227,805
U.S. agency securities	—		33,114		—		33,114
U.S. agency mortgage-backed securities	—		456,037		—		456,037
Municipal debt securities	—		465,255		—		465,255
Corporate debt securities	—		611,728		—		611,728
Residential and commercial mortgage securities	—		79,407		—		79,407
Asset-backed securities	—		167,922		—		167,922
Money market funds	263,797		—		—		263,797
Total assets at fair value	$	491,602	$	1,813,463	$	—	$	2,305,065