Deposits - Maturity Distribution of Time Certificates of Deposits (Details) $ in Thousands	Jun. 30, 2017 USD ($)
Maturity distribution of time certificates of deposit
Three months or less	$ 1,950,694
Over three through six months	818,785
Over six through twelve months	662,445
One to two years	210,000
Two to three years	172,255
Three to four years	142,260
Four to five years	111,602
Thereafter	18
Total	4,068,059
Under $250,000
Maturity distribution of time certificates of deposit
Three months or less	236,404
Over three through six months	269,544
Over six through twelve months	267,980
One to two years	126,118
Two to three years	124,299
Three to four years	92,840
Four to five years	81,989
Thereafter	18
Total	1,199,192
$250,000 or More
Maturity distribution of time certificates of deposit
Three months or less	1,714,290
Over three through six months	549,241
Over six through twelve months	394,465
One to two years	83,882
Two to three years	47,956
Three to four years	49,420
Four to five years	29,613
Total	$ 2,868,867