Segment Information - Additional Information (Detail) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2016 USD ($)	Jun. 30, 2015 USD ($)	Jun. 30, 2016 USD ($) Segment	Jun. 30, 2015 USD ($)	Dec. 31, 2015 USD ($)
Segment Reporting Information [Line Items]
Net income	$ 39,122	$ 26,156	$ 66,099	$ 47,062
Total assets	$ 14,420,262	$ 12,074,404	$ 14,420,262	$ 12,074,404	$ 11,991,527
Number of reportable operating segment | Segment			2
Community Banking Segment [Member]
Segment Reporting Information [Line Items]
Number of reportable operating segment | Segment			1
Insurance Segments [Member]
Segment Reporting Information [Line Items]
Net income					2,100
Total assets					$ 61,800