Securities Available for Sale - Continuous loss (Details) $ in Thousands	Sep. 30, 2017 USD ($) position	Dec. 31, 2016 USD ($) position
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 months	$ 63,203	$ 121,290
Unrealized Losses, Less than 12 months	(59)	(196)
Fair Value, 12 months or longer	8,347	17,518
Unrealized Losses, 12 months or longer	(10)	(51)
Fair Value	71,550	138,808
Unrealized Losses	$ (69)	$ (247)
Number of positions with unrealized losses | position	41	72
Corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 months	$ 37,291	$ 107,862
Unrealized Losses, Less than 12 months	(20)	(185)
Fair Value, 12 months or longer	8,347	11,682
Unrealized Losses, 12 months or longer	(10)	(14)
Fair Value	45,638	119,544
Unrealized Losses	(30)	(199)
Asset-backed securities related to Company- sponsored securitization transactions (1)
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 months	19,187
Unrealized Losses, Less than 12 months	(32)
Fair Value, 12 months or longer	0
Unrealized Losses, 12 months or longer	0
Fair Value	19,187
Unrealized Losses	(32)
Asset-backed securities
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 months	4,233	6,628
Unrealized Losses, Less than 12 months	(3)	(8)
Fair Value, 12 months or longer	0	1,870
Unrealized Losses, 12 months or longer	0	(1)
Fair Value	4,233	8,498
Unrealized Losses	(3)	(9)
U.S. Treasury securities
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 months	2,492
Unrealized Losses, Less than 12 months	(4)
Fair Value, 12 months or longer	0
Unrealized Losses, 12 months or longer	0
Fair Value	2,492
Unrealized Losses	$ (4)
Other securities
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 months		6,800
Unrealized Losses, Less than 12 months		(3)
Fair Value, 12 months or longer		3,966
Unrealized Losses, 12 months or longer		(36)
Fair Value		10,766
Unrealized Losses		$ (39)