Securities Available for Sale - Continuous loss (Details) $ in Thousands	Sep. 30, 2015 USD ($) position
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 months	$ 308,034
Unrealized Losses, Less than 12 months	(1,189)
Fair Value, 12 months or longer	0
Unrealized Losses, 12 months or longer	0
Fair Value	308,034
Unrealized Losses	$ (1,189)
Number of positions with unrealized losses | position	142
Corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 months	$ 241,480
Unrealized Losses, Less than 12 months	(1,144)
Fair Value, 12 months or longer	0
Unrealized Losses, 12 months or longer	0
Fair Value	241,480
Unrealized Losses	(1,144)
Asset-backed securities
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 months	49,955
Unrealized Losses, Less than 12 months	(35)
Fair Value, 12 months or longer	0
Unrealized Losses, 12 months or longer	0
Fair Value	49,955
Unrealized Losses	(35)
U.S. agency securities
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 months	11,600
Unrealized Losses, Less than 12 months	(4)
Fair Value, 12 months or longer	0
Unrealized Losses, 12 months or longer	0
Fair Value	11,600
Unrealized Losses	(4)
Other securities
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 months	4,999
Unrealized Losses, Less than 12 months	(6)
Fair Value, 12 months or longer	0
Unrealized Losses, 12 months or longer	0
Fair Value	4,999
Unrealized Losses	$ (6)