Pension, Savings, And Other Employee Benefits - Narrative (Details) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2019 USD ($) pension_plan	Dec. 31, 2018 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, expected contributions by employer remainder of year	$ 5.2
Savings Plan
Defined Benefit Plan Disclosure [Line Items]
Employer investment in qualified defined contribution plan	100.00%
Maximum percent of employee pre-tax contributions that may be matched by the Company (percent)	6.00%
Qualified Plan | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Estimated social security benefits age	65 years
Nonqualified Plan | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, contributions by employer		$ 5.8
Capital Bank Financial Corp | Qualified Plan | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Number of additional qualified pension plans | pension_plan	2
Defined benefit plan, benefit obligation		17.1
Defined benefit plan, fair value of plan assets		$ 16.5