Investments (Details 3) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Available-for-sale Securities, Amortized Cost Basis [Abstract]
Due in one year or less	$ 5,783
Due after one year through five years	106,649
Due after five years through ten years	282,802
Due after ten years	1,275,557
Total securities available-for-sale	1,670,791	$ 1,522,871
Fair Value Disclosures [Abstract]
Due in one year or less	5,810
Due after one year through five years	108,045
Due after five years through ten years	291,215
Due after ten years	1,293,088
Total securities available-for-sale	$ 1,698,158	$ 1,567,177