Purchased Loans (Details 5) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Loan portfolio by risk-rating grades
Total	$ 6,202,709	$ 5,413,462
Commercial, financial, agricultural
Loan portfolio by risk-rating grades
Total	717,490	636,837
Real estate – construction
Loan portfolio by risk-rating grades
Total	552,679	357,665
Real estate – 1-4 family mortgage
Loan portfolio by risk-rating grades
Total	1,878,177	1,735,323
Real estate – commercial mortgage
Loan portfolio by risk-rating grades
Total	2,898,895	2,533,729
Installment loans to individuals
Loan portfolio by risk-rating grades
Total	155,468	149,908
Purchased
Loan portfolio by risk-rating grades
Total	1,489,137	1,583,028
Purchased | Internal Noninvestment Grade
Loan portfolio by risk-rating grades
Total	901,252	893,088
Purchased | Pass
Loan portfolio by risk-rating grades
Total	877,440	876,619
Purchased | Watch
Loan portfolio by risk-rating grades
Total	21,120	9,934
Purchased | Substandard
Loan portfolio by risk-rating grades
Total	2,692	6,535
Purchased | Commercial, financial, agricultural
Loan portfolio by risk-rating grades
Total	128,200	151,430
Purchased | Commercial, financial, agricultural | Internal Noninvestment Grade
Loan portfolio by risk-rating grades
Total	106,638	129,998
Purchased | Commercial, financial, agricultural | Pass
Loan portfolio by risk-rating grades
Total	102,777	128,602
Purchased | Commercial, financial, agricultural | Watch
Loan portfolio by risk-rating grades
Total	2,370	352
Purchased | Commercial, financial, agricultural | Substandard
Loan portfolio by risk-rating grades
Total	1,491	1,044
Purchased | Real estate – construction
Loan portfolio by risk-rating grades
Total	68,753	65,964
Purchased | Real estate – construction | Internal Noninvestment Grade
Loan portfolio by risk-rating grades
Total	63,846	49,436
Purchased | Real estate – construction | Pass
Loan portfolio by risk-rating grades
Total	61,206	49,436
Purchased | Real estate – construction | Watch
Loan portfolio by risk-rating grades
Total	2,640	0
Purchased | Real estate – construction | Substandard
Loan portfolio by risk-rating grades
Total	0	0
Purchased | Real estate – 1-4 family mortgage
Loan portfolio by risk-rating grades
Total	452,447	531,095
Purchased | Real estate – 1-4 family mortgage | Internal Noninvestment Grade
Loan portfolio by risk-rating grades
Total	113,294	144,738
Purchased | Real estate – 1-4 family mortgage | Pass
Loan portfolio by risk-rating grades
Total	105,265	136,417
Purchased | Real estate – 1-4 family mortgage | Watch
Loan portfolio by risk-rating grades
Total	7,665	4,549
Purchased | Real estate – 1-4 family mortgage | Substandard
Loan portfolio by risk-rating grades
Total	364	3,772
Purchased | Real estate – commercial mortgage
Loan portfolio by risk-rating grades
Total	823,758	804,680
Purchased | Real estate – commercial mortgage | Internal Noninvestment Grade
Loan portfolio by risk-rating grades
Total	617,360	568,916
Purchased | Real estate – commercial mortgage | Pass
Loan portfolio by risk-rating grades
Total	608,192	562,164
Purchased | Real estate – commercial mortgage | Watch
Loan portfolio by risk-rating grades
Total	8,445	5,033
Purchased | Real estate – commercial mortgage | Substandard
Loan portfolio by risk-rating grades
Total	723	1,719
Purchased | Installment loans to individuals
Loan portfolio by risk-rating grades
Total	15,979	29,859
Purchased | Installment loans to individuals | Internal Noninvestment Grade
Loan portfolio by risk-rating grades
Total	114	0
Purchased | Installment loans to individuals | Pass
Loan portfolio by risk-rating grades
Total	0	0
Purchased | Installment loans to individuals | Watch
Loan portfolio by risk-rating grades
Total	0	0
Purchased | Installment loans to individuals | Substandard
Loan portfolio by risk-rating grades
Total	$ 114	$ 0