Deposits - Maturity Distribution of Time Certificates of Deposits (Details) $ in Thousands	Mar. 31, 2019 USD ($)
Maturity distribution of time certificates of deposit
Three months or less	$ 965,899
Over three through six months	636,907
Over six through twelve months	785,146
One to two years	204,753
Two to three years	161,424
Three to four years	76,355
Four to five years	80,752
Thereafter	54
Total	2,911,290
Under $250,000
Maturity distribution of time certificates of deposit
Three months or less	306,984
Over three through six months	149,913
Over six through twelve months	383,212
One to two years	118,264
Two to three years	112,532
Three to four years	54,408
Four to five years	67,061
Thereafter	54
Total	1,192,428
$250,000 or More
Maturity distribution of time certificates of deposit
Three months or less	658,915
Over three through six months	486,994
Over six through twelve months	401,934
One to two years	86,489
Two to three years	48,892
Three to four years	21,947
Four to five years	13,691
Total	$ 1,718,862