Commitments and Contingencies - Commitments and Letters of Credit (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Commitment And Contingencies [Line Items]
Commitments and letters of credit	$ 1,717,530	$ 1,232,212
Standby Letters of Credit
Commitment And Contingencies [Line Items]
Commitments and letters of credit	97,676	73,584
Commitments to Extend Credit
Commitment And Contingencies [Line Items]
Commitments and letters of credit	$ 1,619,854	$ 1,158,628