Employee Benefit Plans (Amounts Recognized in the Financial Statements) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
BancShares Plan
Amounts recognized in the consolidated balance sheets
Other assets	$ 0	$ 0
Other liabilities	72,611	61,477
Net asset (liability) recognized	72,611	61,477
Amount recognized in accumulated other comprehensive income
Net loss (gain)	119,766	70,358
Less prior service cost	347	556
Accumulated other comprehensive loss, excluding income taxes	120,113	70,914
Actuarial loss	8,938
Prior service cost	210
Total	9,148
Bancorporation Plan
Amounts recognized in the consolidated balance sheets
Other assets	0	0
Other liabilities	4,747	7,652
Net asset (liability) recognized	4,747	7,652
Amount recognized in accumulated other comprehensive income
Net loss (gain)	21,661	7,505
Less prior service cost	0	0
Accumulated other comprehensive loss, excluding income taxes	21,661	$ 7,505
Actuarial loss	855
Prior service cost	0
Total	$ 855