Deposits - Maturity Distribution of Time Certificates of Deposits (Details) $ in Thousands	Jun. 30, 2018 USD ($)
Maturity distribution of time certificates of deposit
Three months or less	$ 1,496,591
Over three through six months	925,555
Over six through twelve months	925,962
One to two years	198,757
Two to three years	153,710
Three to four years	105,531
Four to five years	83,124
Thereafter	113
Total	3,889,343
Under $250,000
Maturity distribution of time certificates of deposit
Three months or less	205,600
Over three through six months	241,520
Over six through twelve months	427,839
One to two years	122,322
Two to three years	101,819
Three to four years	78,520
Four to five years	55,176
Thereafter	113
Total	1,232,909
$250,000 or More
Maturity distribution of time certificates of deposit
Three months or less	1,290,991
Over three through six months	684,035
Over six through twelve months	498,123
One to two years	76,435
Two to three years	51,891
Three to four years	27,011
Four to five years	27,948
Total	$ 2,656,434