XML 47 R37.htm IDEA: XBRL DOCUMENT v3.19.1
Investments, Summary of Investments (Details) - USD ($)
$ in Thousands
3 Months Ended 12 Months Ended
Mar. 31, 2019
Dec. 31, 2018
Summary of Investments [Abstract]    
Cost $ 1,212 [1] $ 1,212
Gross unrealized gains 0 137
Gross unrealized losses (244) 0
Estimated fair value 968 1,349
Cost 1,920,577 1,874,529
Gross unrealized gains 2,045 556
Gross unrealized losses (1,600) (4,068)
Estimated fair value 1,921,022 1,871,017
Available-for-sale Securities [Member]    
Summary of Investments [Abstract]    
Cost [1] 1,919,365 1,873,317
Gross unrealized gains 2,045 419
Gross unrealized losses (1,356) (4,068)
Estimated fair value 1,920,054 1,869,668
Available-for-sale Securities [Member] | Securities with Maturity of One Year or Less [Member]    
Summary of Investments [Abstract]    
Cost [1] 1,388,864 1,433,930
Gross unrealized gains 518 31
Gross unrealized losses (761) (2,362)
Estimated fair value 1,388,621 1,431,599
Available-for-sale Securities [Member] | Securities with Maturity of More than One Year [Member]    
Summary of Investments [Abstract]    
Cost [1] 530,501 439,387
Gross unrealized gains 1,527 388
Gross unrealized losses (595) (1,706)
Estimated fair value 531,433 438,069
Corporate Debt Securities [Member] | Securities with Maturity of One Year or Less [Member]    
Summary of Investments [Abstract]    
Cost [1] 869,483 [2] 956,879
Gross unrealized gains 326 13
Gross unrealized losses (531) (1,858)
Estimated fair value 869,278 955,034
Corporate Debt Securities [Member] | Securities with Maturity of More than One Year [Member]    
Summary of Investments [Abstract]    
Cost [1] 360,976 299,018
Gross unrealized gains 1,236 194
Gross unrealized losses (336) (1,286)
Estimated fair value 361,876 297,926
Debt Securities issued by U.S. Government Agencies [Member] | Securities with Maturity of One Year or Less [Member]    
Summary of Investments [Abstract]    
Cost [1] 124,744 168,839
Gross unrealized gains 71 3
Gross unrealized losses (15) (104)
Estimated fair value 124,800 168,738
Debt Securities issued by U.S. Government Agencies [Member] | Securities with Maturity of More than One Year [Member]    
Summary of Investments [Abstract]    
Cost [1] 120,341 107,789
Gross unrealized gains 279 194
Gross unrealized losses (112) (109)
Estimated fair value 120,508 107,874
Debt Securities issued by the U.S. Treasury [Member] | Securities with Maturity of One Year or Less [Member]    
Summary of Investments [Abstract]    
Cost [1] 328,340 [2] 244,640
Gross unrealized gains 110 15
Gross unrealized losses (12) (77)
Estimated fair value 328,438 244,578
Debt Securities issued by the U.S. Treasury [Member] | Securities with Maturity of More than One Year [Member]    
Summary of Investments [Abstract]    
Cost 33,569 [1] 15,600
Gross unrealized gains 12 0
Gross unrealized losses (22) (24)
Estimated fair value 33,559 15,576
Debt Securities issued by States of the U.S. and Political Subdivisions of the States [Member] | Securities with Maturity of One Year or Less [Member]    
Summary of Investments [Abstract]    
Cost [1],[2] 63,366 63,572
Gross unrealized gains 10 0
Gross unrealized losses (203) (323)
Estimated fair value 63,173 63,249
Debt Securities issued by States of the U.S. and Political Subdivisions of the States [Member] | Securities with Maturity of More than One Year [Member]    
Summary of Investments [Abstract]    
Cost [1] 15,615 16,980
Gross unrealized gains 0 0
Gross unrealized losses (125) (287)
Estimated fair value 15,490 $ 16,693
Other Municipal Debt Securities [Member] | Securities with Maturity of One Year or Less [Member]    
Summary of Investments [Abstract]    
Cost [1] 2,931  
Gross unrealized gains 1  
Gross unrealized losses 0  
Estimated fair value $ 2,932  
[1] Our available-for-sale securities are held at amortized cost.
[2] Includes investments classified as cash equivalents on our condensed consolidated balance sheet.