Securities - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2016 USD ($) Holdings	Dec. 31, 2015 USD ($) Holdings	Dec. 31, 2014 USD ($)
Amortized Cost and Fair Value Debt Securities [Abstract]
Trading securities, at fair value	$ 7,071,000	$ 6,451,000
Maximum percentage of equity of one issuer	10.00%
Number of holdings greater than specified percentage of equity | Holdings	0	0
Securities with aggregate fair values	$ 1,200,000,000	$ 1,000,000,000
Proceeds from sale of available-for-sale securities	277,225,000	635,609,000	$ 16,249,000
Net unrealized gains (losses) on available-for-sale securities included in AOCI	(9,900,000)	(4,200,000)	$ 2,900,000
Impaired loss relating to securities	0
Federal home loan bank stock, Total	$ 46,400,000	$ 45,500,000