Acquisition Activity - Additional Information (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended	0 Months Ended
	Mar. 31, 2015	Feb. 28, 2015	Dec. 31, 2014	Dec. 31, 2013
Business Acquisition [Line Items]
Goodwill	$ 621,723		$ 517,526	$ 401,872
Maximum period for subject to change estimated fair values after acquisition date	1 year
Florida Bank Group, Inc. [Member]
Business Acquisition [Line Items]
Cash received per share		$ 7.81
Shares received		0.149
Business combination date of acquisition	Feb. 28, 2015
Total consideration paid	90,485	90,500
Goodwill	14,686	14,700
Number of bank offices	12
Old Florida Bancshares, Inc. [Member]
Business Acquisition [Line Items]
Shares received	0.34
Business combination date of acquisition	Mar. 31, 2015
Total consideration paid	253,152
Goodwill	$ 89,511
Number of bank offices	14
Georgia Commerce Bancshares Inc [Member]
Business Acquisition [Line Items]
Shares received	0.6134