Investment Securities - Gross Unrealized Losses and Fair Value, Aggregated by Investment Category (Detail) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Less Than 12 Months, Fair Value	$ 70,982	$ 334,656
Less Than 12 Months, Unrealized Losses	(5,296)	(7,863)
12 Months or More, Fair Value	56,610	57,363
12 Months or More, Unrealized Losses	(1,307)	(2,207)
Fair Value, Total	127,592	392,019
Gross Unrealized Losses	(6,603)	(10,070)
Corporate notes
Schedule of Available-for-sale Securities [Line Items]
Less Than 12 Months, Fair Value	18,718	9,748
Less Than 12 Months, Unrealized Losses	(209)	(178)
12 Months or More, Fair Value	0	0
12 Months or More, Unrealized Losses	0	0
Fair Value, Total	18,718	9,748
Gross Unrealized Losses	(209)	(178)
Agency-guaranteed residential mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Less Than 12 Months, Fair Value	13,858	102,832
Less Than 12 Months, Unrealized Losses	(23)	(535)
12 Months or More, Fair Value	56,604	57,357
12 Months or More, Unrealized Losses	(1,306)	(2,206)
Fair Value, Total	70,462	160,189
Gross Unrealized Losses	(1,329)	(2,741)
Agency-guaranteed commercial real estate mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Less Than 12 Months, Fair Value	20,954	202,870
Less Than 12 Months, Unrealized Losses	(9)	(3,849)
12 Months or More, Fair Value	0	0
12 Months or More, Unrealized Losses	0	0
Fair Value, Total	20,954	202,870
Gross Unrealized Losses	(9)	(3,849)
Equity securities
Schedule of Available-for-sale Securities [Line Items]
Less Than 12 Months, Fair Value	17,452	19,206
Less Than 12 Months, Unrealized Losses	(5,055)	(3,301)
12 Months or More, Fair Value	6	6
12 Months or More, Unrealized Losses	(1)	(1)
Fair Value, Total	17,458	19,212
Gross Unrealized Losses	$ (5,056)	$ (3,302)