Fair Value - Changes in Fair Value for Items Measured at Fair Value Pursuant to Election of the Fair Value (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Schedule of Trading Securities and Other Trading Assets [Line Items]
Interest Income	$ 109,917	$ 107,803	$ 99,340	$ 85,643	$ 85,922	$ 97,104	$ 92,097	$ 90,993	$ 402,703	$ 366,116	$ 366,370
Interest (Expense)	$ (11,932)	$ (11,910)	$ (10,903)	$ (9,686)	$ (9,038)	$ (8,567)	$ (7,867)	$ (7,601)	(44,431)	(33,073)	$ (23,359)
Residential Loans Held for Sale [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other Gains and (Losses)									(103)	(140)
Interest Income									0	0
Interest (Expense)									0	0
Total Changes in Fair Values Included in Current Period Earnings									$ (103)	$ (140)