Investment Securities (Narrative) (Detail)	3 Months Ended
	Mar. 31, 2017 USD ($) position security	Mar. 31, 2016 USD ($)	Dec. 31, 2016 USD ($) position security
Schedule of Held-to-maturity Securities [Line Items]
Securities available for sale, at fair value	$ 1,048,119,000		$ 1,040,386,000
Investment securities held to maturity	$ 489,114,000		$ 488,183,000
Total number of all held to maturity and available for sale securities in an unrealized loss position | security	360		419
Amortized cost	$ 1,047,690,000		$ 1,041,247,000
Proceeds from the sale of securities available for sale	0	$ 2,100,000
Gross gains		95,000
Gross losses		0
Proceeds from calls on securities available for sale	$ 0	0
Number of securities in an unrealized loss position | position	90		87
Other-than-temporary impairment charges, net	$ 0	0
Proceeds from calls of held to maturity securities	12,800,000	516,000
Recognized gain on calls of securities, held-to-maturity portfolio	0	1,000
Recognized loss on calls of securities held-to-maturity portfolio	0	$ 0
Held-to-maturity securities, fair value	$ 492,863,000		$ 489,287,000
Number of securities in an unrealized loss position | position	270		332
Private Label Mortgage-Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Number of securities in an unrealized loss position | position	2
Mortgage-Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Securities available for sale, at fair value	$ 967,318,000		$ 951,861,000
Investment securities held to maturity	680,000		893,000
Amortized cost	967,483,000		952,992,000
Held-to-maturity securities, amortized cost	680,000
Held-to-maturity securities, fair value	705,000		924,000
Equity Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Securities available for sale, at fair value	558,000		549,000
Amortized cost	397,000		$ 397,000
Private Label Mortgage Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	74,000
Unrealized losses	$ 3,000