Deposits - Maturity Distribution of Time Certificates of Deposits (Details) $ in Thousands	Sep. 30, 2018 USD ($)
Maturity distribution of time certificates of deposit
Three months or less	$ 1,270,845
Over three through six months	733,388
Over six through twelve months	769,781
One to two years	203,769
Two to three years	145,263
Three to four years	98,708
Four to five years	68,658
Thereafter	87
Total	3,290,499
Under $250,000
Maturity distribution of time certificates of deposit
Three months or less	243,274
Over three through six months	271,511
Over six through twelve months	365,416
One to two years	123,127
Two to three years	106,088
Three to four years	64,676
Four to five years	51,952
Thereafter	87
Total	1,226,131
$250,000 or More
Maturity distribution of time certificates of deposit
Three months or less	1,027,571
Over three through six months	461,877
Over six through twelve months	404,365
One to two years	80,642
Two to three years	39,175
Three to four years	34,032
Four to five years	16,706
Total	$ 2,064,368