Deposits - Maturity Distribution of Time Certificates of Deposits (Details) $ in Thousands	Sep. 30, 2017 USD ($)
Maturity distribution of time certificates of deposit
Three months or less	$ 2,148,749
Over three through six months	1,141,603
Over six through twelve months	578,243
One to two years	363,273
Two to three years	164,602
Three to four years	140,911
Four to five years	107,700
Thereafter	46
Total	4,645,127
Under $250,000
Maturity distribution of time certificates of deposit
Three months or less	276,403
Over three through six months	254,135
Over six through twelve months	259,014
One to two years	140,633
Two to three years	113,747
Three to four years	101,430
Four to five years	68,182
Thereafter	46
Total	1,213,590
$250,000 or More
Maturity distribution of time certificates of deposit
Three months or less	1,872,346
Over three through six months	887,468
Over six through twelve months	319,229
One to two years	222,640
Two to three years	50,855
Three to four years	39,481
Four to five years	39,518
Total	$ 3,431,537