Investment Securities - Gross Unrealized Losses and Fair Value, Aggregated by Investment Category (Detail) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Less Than 12 Months, Fair Value	$ 13,923	$ 334,656
Less Than 12 Months, Unrealized Losses	(78)	(7,863)
12 Months or More, Fair Value	69,762	57,363
12 Months or More, Unrealized Losses	(6,373)	(2,207)
Fair Value, Total	83,685	392,019
Unrealized Losses	(6,451)	(10,070)
Corporate notes
Schedule of Available-for-sale Securities [Line Items]
Less Than 12 Months, Fair Value	13,923	9,748
Less Than 12 Months, Unrealized Losses	(78)	(178)
12 Months or More, Fair Value	0	0
12 Months or More, Unrealized Losses	0	0
Fair Value, Total	13,923	9,748
Unrealized Losses	(78)	(178)
Agency-guaranteed residential mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Less Than 12 Months, Fair Value	0	102,832
Less Than 12 Months, Unrealized Losses	0	(535)
12 Months or More, Fair Value	53,069	57,357
12 Months or More, Unrealized Losses	(552)	(2,206)
Fair Value, Total	53,069	160,189
Unrealized Losses	(552)	(2,741)
Agency-guaranteed commercial real estate mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Less Than 12 Months, Fair Value		202,870
Less Than 12 Months, Unrealized Losses		(3,849)
12 Months or More, Fair Value		0
12 Months or More, Unrealized Losses		0
Fair Value, Total		202,870
Unrealized Losses		(3,849)
Equity securities
Schedule of Available-for-sale Securities [Line Items]
Less Than 12 Months, Fair Value	0	19,206
Less Than 12 Months, Unrealized Losses	0	(3,301)
12 Months or More, Fair Value	16,693	6
12 Months or More, Unrealized Losses	(5,821)	(1)
Fair Value, Total	16,693	19,212
Unrealized Losses	$ (5,821)	$ (3,302)