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, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Schedule of Trading Securities and Other Trading Assets [Line Items]
Interest Income	$ 148,899	$ 153,096	$ 155,230	$ 147,048	$ 146,225	$ 130,842	$ 131,963	$ 128,572	$ 604,273	$ 537,602	$ 437,168
Interest (Expense)	$ (27,654)	$ (32,757)	$ (33,833)	$ (31,870)	$ (29,009)	$ (24,527)	$ (21,773)	$ (19,134)	(126,114)	(94,443)	$ (58,168)
Residential Loans Held for Sale [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other Gains and (Losses)									1,036	(67)
Interest Income									18	6
Interest (Expense)										(10)
Total Changes in Fair Values Included in Current Period Earnings									$ 1,054	$ (71)