Investment Securities - (Narrative) (Detail) $ in Thousands	1 Months Ended	12 Months Ended
	Aug. 31, 2015 USD ($)	Dec. 31, 2015 USD ($) security	Dec. 31, 2014 USD ($) security	Aug. 01, 2015 USD ($)
Investment securities total		$ 1,600,000	$ 2,000,000
Available-for-sale securities		1,157,246	1,479,214
Held-to-maturity securities		$ 427,503	$ 530,590
Mortgage-backed securities as percentage of available-for-sale investment portfolio		100.00%	100.00%
Number of securities | security		66	62
Fair value of available-for-sale securities in an unrealized loss position		$ 752,663	$ 845,988
Proceeds from sales of investment securities available-for-sale		29,747
Fair value of available-for-sale investment securities pledged as collateral		$ 335,800	$ 274,400
Estimated weighted average life of the available-for-sale mortgage-backed securities portfolio		3 years 7 months 6 days	3 years 6 months
Other securities having no contractual maturity date		$ 400
Number of held-to-maturity securities in unrealized loss positions | security		16	12
Fair value of held-to-maturity securities in an unrealized loss position		$ 109,856	$ 110,278
Held-to-maturity investment securities pledged as collateral		$ 156,500	$ 88,300
Estimated weighted average expected life of the held-to-maturity mortgage-backed securities portfolio		3 years 8 months 12 days	3 years 4 months 24 days
Pine River Bank Corporation [Member]
Available-for-sale securities acquired				$ 30,093
Proceeds from sales of investment securities available-for-sale	$ 29,800