Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 247,105	$ 158,801	$ 116,073
Unrealized gains (losses) on securities:
Change in unrealized holding gains (losses), net	21,139	(77,794)	(13,393)
Less: Reclassifications adjustment for net gains included in net income	(4,192)	(8,509)	(10,402)
Change in unrealized gains (losses) on securities during the period	16,947	(86,303)	(23,795)
Change in unrealized losses on derivative hedges	(1,050)	(516)	(10)
Income tax (expense) benefit	(3,880)	32,995	9,081
Other comprehensive income (loss)	12,017	(53,824)	(14,724)
Comprehensive income	$ 259,122	$ 104,977	$ 101,349