Deposits - Total deposits - (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015
Deposits Abstract
Certificates of deposit	$ 1,033,109	$ 1,092,750	$ 1,187,908
Interest-bearing demand deposits	3,338,433	3,293,942	3,009,005
Non-interest bearing demand deposits	2,020,632	1,976,480	1,757,302
Savings deposits	766,752	735,961	677,056
Other time deposits	3,022	1,295	2,386
Total deposits	$ 7,161,948	$ 7,100,428	$ 6,633,657