Securities Available for Sale - Continuous loss (Details) $ in Thousands	Mar. 31, 2016 USD ($) position	Dec. 31, 2015 USD ($) position
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 months	$ 223,203	$ 291,478
Unrealized Losses, Less than 12 months	(994)	(1,674)
Fair Value, 12 months or longer	0	0
Unrealized Losses, 12 months or longer	0	0
Fair Value	223,203	291,478
Unrealized Losses	$ (994)	$ (1,674)
Number of positions with unrealized losses | position	109	141
Corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 months	$ 166,436	$ 212,018
Unrealized Losses, Less than 12 months	(877)	(1,494)
Fair Value, 12 months or longer	0	0
Unrealized Losses, 12 months or longer	0	0
Fair Value	166,436	212,018
Unrealized Losses	(877)	(1,494)
Asset-backed securities
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 months	35,235	54,409
Unrealized Losses, Less than 12 months	(42)	(134)
Fair Value, 12 months or longer	0	0
Unrealized Losses, 12 months or longer	0	0
Fair Value	35,235	54,409
Unrealized Losses	(42)	(134)
U.S. agency securities
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 months	14,582	14,578
Unrealized Losses, Less than 12 months	(21)	(25)
Fair Value, 12 months or longer	0	0
Unrealized Losses, 12 months or longer	0	0
Fair Value	14,582	14,578
Unrealized Losses	(21)	(25)
U.S. Treasury securities
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 months		3,485
Unrealized Losses, Less than 12 months		(4)
Fair Value, 12 months or longer		0
Unrealized Losses, 12 months or longer		0
Fair Value		3,485
Unrealized Losses		(4)
Other securities
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 months	6,950	6,988
Unrealized Losses, Less than 12 months	(54)	(17)
Fair Value, 12 months or longer	0	0
Unrealized Losses, 12 months or longer	0	0
Fair Value	6,950	6,988
Unrealized Losses	$ (54)	$ (17)