Purchased Loans (Details 5) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Loan portfolio by risk-rating grades
Total	$ 6,371,007	$ 6,202,709
Commercial, financial, agricultural
Loan portfolio by risk-rating grades
Total	760,582	717,490
Real estate – construction
Loan portfolio by risk-rating grades
Total	460,807	552,679
Real estate – 1-4 family mortgage
Loan portfolio by risk-rating grades
Total	1,952,394	1,878,177
Real estate – commercial mortgage
Loan portfolio by risk-rating grades
Total	3,040,963	2,898,895
Installment loans to individuals
Loan portfolio by risk-rating grades
Total	156,261	155,468
Purchased loans
Loan portfolio by risk-rating grades
Total	1,312,109	1,489,137
Purchased loans | Internal Noninvestment Grade
Loan portfolio by risk-rating grades
Total	783,030	901,252
Purchased loans | Pass
Loan portfolio by risk-rating grades
Total	765,799	877,440
Purchased loans | Watch
Loan portfolio by risk-rating grades
Total	15,642	21,120
Purchased loans | Substandard
Loan portfolio by risk-rating grades
Total	1,589	2,692
Purchased loans | Commercial, financial, agricultural | Internal Noninvestment Grade
Loan portfolio by risk-rating grades
Total	78,968	106,638
Purchased loans | Commercial, financial, agricultural | Pass
Loan portfolio by risk-rating grades
Total	76,505	102,777
Purchased loans | Commercial, financial, agricultural | Watch
Loan portfolio by risk-rating grades
Total	2,054	2,370
Purchased loans | Commercial, financial, agricultural | Substandard
Loan portfolio by risk-rating grades
Total	409	1,491
Purchased loans | Real estate – construction | Internal Noninvestment Grade
Loan portfolio by risk-rating grades
Total	35,007	63,846
Purchased loans | Real estate – construction | Pass
Loan portfolio by risk-rating grades
Total	35,007	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	95,354	113,294
Purchased loans | Real estate – 1-4 family mortgage | Pass
Loan portfolio by risk-rating grades
Total	89,147	105,265
Purchased loans | Real estate – 1-4 family mortgage | Watch
Loan portfolio by risk-rating grades
Total	6,003	7,665
Purchased loans | Real estate – 1-4 family mortgage | Substandard
Loan portfolio by risk-rating grades
Total	204	364
Purchased loans | Real estate – commercial mortgage | Internal Noninvestment Grade
Loan portfolio by risk-rating grades
Total	573,697	617,360
Purchased loans | Real estate – commercial mortgage | Pass
Loan portfolio by risk-rating grades
Total	565,140	608,192
Purchased loans | Real estate – commercial mortgage | Watch
Loan portfolio by risk-rating grades
Total	7,585	8,445
Purchased loans | Real estate – commercial mortgage | Substandard
Loan portfolio by risk-rating grades
Total	972	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