Shareholders' Equity, Dividends Restrictions and Other Regulatory Matters (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2016 USD ($) vote shares	Dec. 31, 2015 USD ($) shares	Dec. 31, 2014 USD ($)
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Capital required for common equity Tier 1 capital to risk-weighted assets	4.50%
Tier 1 Risk Based Capital Required for Capital Adequacy to Risk Weighted Assets	6.00%
Capital Required for Capital Adequacy to Risk Weighted Assets	8.00%
Leverage Capital Required Ratio To Tangible Assets	4.00%
Percent Of Trust Preferred Securities Excluded From Tier One Starting In 2013	75.00%
Remaining Percent of Trust Preferred Securities Excluded from Tier One After 2015	25.00%
Tier 2 capital	$ 3,000	$ 6,000
Subordinated Debt, Annual Tier 2 Discount Percentage	20.00%
Maximum Undivided Profits Elgible For Dividend Payment Without Changing Well Capitalized Status	$ 928,700
Average Required Maintence Of Non Interst Bearing Reserve Balance	$ 575,700
Capital Conservation Buffer, Annual Percentage Increase	0.625%
Capital Conservation Buffer	2.50%
Common Class A [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Votes per share of common stock | vote	1
Stock Repurchase Program, Number of Shares Authorized to be Repurchased | shares	200,000
Stock Repurchased During Period, Shares | shares		0
Class B Common Stock
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Votes per share of common stock | vote	16
Stock Repurchased and Retired During Period, Shares | shares	0	0
Parent
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Dividends from subsidiaries	$ 90,055	$ 75,006	$ 30,000
BancShares [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Tier 1 Capital for Capital Adequacy	2,995,557	2,831,242
Capital Required for Capital Adequacy	3,339,986	3,140,212
Leverage Capital Required for Capital Adequacy	$ 2,995,557	$ 2,831,242
Tier 1 Risk Based Capital to Risk Weighted Assets	12.42%	12.65%
Capital to Risk Weighted Assets	13.85%	14.03%
Leverage Capital to Average Assets	9.05%	8.96%
Tier 1 Risk Based Capital Required to be Well Capitalized to Risk Weighted Assets	8.00%	8.00%
Common equity Tier 1	$ 2,995,557	$ 2,799,163
Common equity Tier 1 to risk-weighted assets	12.42294%	12.50965%
Common equity Tier 1 required to be well capitalized to risk-weighted assets	6.50%	6.50%
Capital Required to be Well Capitalized	10.00%	10.00%
Leverage Capital Required to be Well Capitalized to Average Assets	5.00%	5.00%
Capital Conservation Buffer	5.85%
FCB [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Tier 1 Capital for Capital Adequacy	$ 2,942,829	$ 2,821,475
Capital Required for Capital Adequacy	3,172,757	3,038,070
Leverage Capital Required for Capital Adequacy	$ 2,942,829	$ 2,821,475
Tier 1 Risk Based Capital to Risk Weighted Assets	12.25%	12.64%
Capital to Risk Weighted Assets	13.21%	13.61%
Leverage Capital to Average Assets	8.94%	8.95%
Tier 1 Risk Based Capital Required to be Well Capitalized to Risk Weighted Assets	8.00%	8.00%
Common equity Tier 1	$ 2,942,829	$ 2,821,475
Common equity Tier 1 to risk-weighted assets	12.25305%	12.63988%
Common equity Tier 1 required to be well capitalized to risk-weighted assets	6.50%	6.50%
Capital Required to be Well Capitalized	10.00%	10.00%
Leverage Capital Required to be Well Capitalized to Average Assets	5.00%	5.00%
Capital Conservation Buffer	5.21%