Reclassifications Out of Accumulated Other Comprehensive Income - Summary of reclassifications (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Securities (losses) gains, net	$ (656)	$ 42	$ 982
Deposits in banks and short-term investments interest revenue	2,012	2,282	2,611
Money market deposit interest expense	(12,097)	(7,033)	(4,982)
Federal Home Loan Bank advances interest expense	(6,345)	(6,095)	(3,676)
Salaries and employee benefits expense	(181,015)	(153,098)	(138,789)
Other expense	(32,514)	(26,961)	(24,742)
Tax benefit (expense)	(49,815)	(105,013)	(62,336)
Net income available to common shareholders	164,927	67,250	100,635
Reclassifications Out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net income available to common shareholders	(2,113)	(4,962)	(2,163)
Reclassifications Out of Accumulated Other Comprehensive Income | Realized gains (losses) on available-for-sale securities
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Securities (losses) gains, net	(656)	42	982
Tax benefit (expense)	132	(14)	(371)
Net income available to common shareholders	(524)	28	611
Reclassifications Out of Accumulated Other Comprehensive Income | Amortization of losses included in net income on available-for-sale securities transferred to held to maturity
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Investment securities interest revenue	(739)	(1,069)	(1,759)
Tax benefit (expense)	180	401	662
Net income available to common shareholders	(559)	(668)	(1,097)
Reclassifications Out of Accumulated Other Comprehensive Income | Amounts included in net income on derivative financial instruments accounted for as cash flow hedges
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Deposits in banks and short-term investments interest revenue	0	0	(7)
Money market deposit interest expense	(499)	(599)	(647)
Federal Home Loan Bank advances interest expense	0	(292)	(1,237)
Total before tax	(499)	(891)	(1,891)
Tax benefit (expense)	129	346	736
Net income available to common shareholders	(370)	(545)	(1,155)
Reclassifications Out of Accumulated Other Comprehensive Income | Reclassification of disproportionate tax effect related to terminated cash flow hedges
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Tax benefit (expense)	0	(3,289)	0
Reclassifications Out of Accumulated Other Comprehensive Income | Prior service cost
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Salaries and employee benefits expense	(666)	(560)	(501)
Reclassifications Out of Accumulated Other Comprehensive Income | Actuarial losses
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Salaries and employee benefits expense	0	(238)	(354)
Other expense	(241)	0	0
Reclassifications Out of Accumulated Other Comprehensive Income | Amortization of prior service cost and actuarial losses included in net periodic pension cost for defined benefit pension plan
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before tax	(907)	(798)	(855)
Tax benefit (expense)	247	310	333
Net income available to common shareholders	$ (660)	$ (488)	$ (522)