Business Combinations - Additional Information (Details) $ / shares in Units, $ in Thousands		3 Months Ended		12 Months Ended
	Feb. 15, 2013 USD ($) $ / shares shares	Mar. 31, 2014 USD ($)	Mar. 31, 2013 USD ($)	Dec. 31, 2015 USD ($) Market	Dec. 31, 2013 USD ($)	Dec. 31, 2014 USD ($)
Business Acquisition [Line Items]
Decrease in goodwill with a corresponding increase in deferred tax asset as measurement period adjustment		$ 7,400
Goodwill				$ 366,156	$ 372,851	$ 365,500
Amortization period of acquired intangible asset				20 years
BancTrust Financial Group, Inc. [Member]
Business Acquisition [Line Items]
Age of acquired entity	26 years
Equity issued, per share of acquired company (in shares) | shares	0.125
Equity issued (in shares) | shares	2,240,000
Business acquisition, equity issued, value assigned	$ 53,500
Business acquisition, closing stock price (in dollars per share) | $ / shares	$ 23.83
Issued value of preferred stock and associated warrant under capital purchase program	$ 50,000
Preferred stock and warrants repurchase amount	52,600
Number of markets entered due to acquisition | Market				15
Decrease in acquired non covered loans as measurement period adjustment					6,800
Decrease in Premises and equipment as measurement period adjustment					627
Decrease in other real estate as measurement period adjustment					2,600
Increase in deferred tax asset as measurement period adjustment					3,400
Increase in goodwill as measurement period adjustment					6,300
Transfer to other real estate as measurement period adjustment					$ 1,600
Goodwill	$ 74,247
Amortization period of acquired intangible asset				10 years
Business acquisition, total transaction expenses			$ 9,400
Business acquisition, severance expense			1,400
Business acquisition, contract termination and other expenses			$ 7,900