Purchased Loans (Details 5) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Loan portfolio by risk-rating grades
Total	$ 6,235,805	$ 6,202,709
Commercial, financial, agricultural
Loan portfolio by risk-rating grades
Total	741,466	717,490
Real estate – construction
Loan portfolio by risk-rating grades
Total	413,734	552,679
Real estate – 1-4 family mortgage
Loan portfolio by risk-rating grades
Total	1,917,567	1,878,177
Real estate – commercial mortgage
Loan portfolio by risk-rating grades
Total	3,008,429	2,898,895
Installment loans to individuals
Loan portfolio by risk-rating grades
Total	154,609	155,468
Purchased loans
Loan portfolio by risk-rating grades
Total	1,401,720	1,489,137
Purchased loans | Internal Noninvestment Grade
Loan portfolio by risk-rating grades
Total	846,561	901,252
Purchased loans | Pass
Loan portfolio by risk-rating grades
Total	827,441	877,440
Purchased loans | Watch
Loan portfolio by risk-rating grades
Total	16,544	21,120
Purchased loans | Substandard
Loan portfolio by risk-rating grades
Total	2,576	2,692
Purchased loans | Commercial, financial, agricultural | Internal Noninvestment Grade
Loan portfolio by risk-rating grades
Total	92,904	106,638
Purchased loans | Commercial, financial, agricultural | Pass
Loan portfolio by risk-rating grades
Total	89,802	102,777
Purchased loans | Commercial, financial, agricultural | Watch
Loan portfolio by risk-rating grades
Total	1,959	2,370
Purchased loans | Commercial, financial, agricultural | Substandard
Loan portfolio by risk-rating grades
Total	1,143	1,491
Purchased loans | Lease financing | Internal Noninvestment Grade
Loan portfolio by risk-rating grades
Total	0	0
Purchased loans | Lease financing | Pass
Loan portfolio by risk-rating grades
Total	0	0
Purchased loans | Lease financing | Watch
Loan portfolio by risk-rating grades
Total	0	0
Purchased loans | Lease financing | Substandard
Loan portfolio by risk-rating grades
Total	0	0
Purchased loans | Real estate – construction | Internal Noninvestment Grade
Loan portfolio by risk-rating grades
Total	34,405	63,846
Purchased loans | Real estate – construction | Pass
Loan portfolio by risk-rating grades
Total	34,405	61,206
Purchased loans | Real estate – construction | Watch
Loan portfolio by risk-rating grades
Total	0	2,640
Purchased loans | Real estate – construction | Substandard
Loan portfolio by risk-rating grades
Total	0	0
Purchased loans | Real estate – 1-4 family mortgage | Internal Noninvestment Grade
Loan portfolio by risk-rating grades
Total	108,949	113,294
Purchased loans | Real estate – 1-4 family mortgage | Pass
Loan portfolio by risk-rating grades
Total	101,652	105,265
Purchased loans | Real estate – 1-4 family mortgage | Watch
Loan portfolio by risk-rating grades
Total	6,578	7,665
Purchased loans | Real estate – 1-4 family mortgage | Substandard
Loan portfolio by risk-rating grades
Total	719	364
Purchased loans | Real estate – commercial mortgage | Internal Noninvestment Grade
Loan portfolio by risk-rating grades
Total	610,299	617,360
Purchased loans | Real estate – commercial mortgage | Pass
Loan portfolio by risk-rating grades
Total	601,582	608,192
Purchased loans | Real estate – commercial mortgage | Watch
Loan portfolio by risk-rating grades
Total	8,007	8,445
Purchased loans | Real estate – commercial mortgage | Substandard
Loan portfolio by risk-rating grades
Total	710	723
Purchased loans | Installment loans to individuals | Internal Noninvestment Grade
Loan portfolio by risk-rating grades
Total	4	114
Purchased loans | Installment loans to individuals | Pass
Loan portfolio by risk-rating grades
Total	0	0
Purchased loans | Installment loans to individuals | Watch
Loan portfolio by risk-rating grades
Total	0	0
Purchased loans | Installment loans to individuals | Substandard
Loan portfolio by risk-rating grades
Total	$ 4	$ 114