Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 60,529	$ 56,959	$ 57,090	$ 114,703
Unrealized gains and losses on debt securities:
Change in unrealized holding gains and losses, net	84,885	107,484	249,001	213,918
Less: Reclassification adjustment for (gains) losses included in net income	(4,006)	1,403	(5,233)	594
Change in unrealized gains and losses on debt securities during the period	80,879	108,887	243,768	214,512
Unrealized gains and losses on derivative hedges:
Change in unrealized gains and losses on derivative hedges	4,612	(3,061)	19,137	(5,149)
Less: Reclassification adjustment for (gains) losses included in net income	(514)	20	254	15
Change in unrealized gains and losses on derivative hedges	4,098	(3,041)	19,391	(5,134)
Other comprehensive income, before tax	84,977	105,846	263,159	209,378
Income tax expense	(20,105)	(25,590)	(62,077)	(50,979)
Other comprehensive income	64,872	80,256	201,082	158,399
Comprehensive income	$ 125,401	$ 137,215	$ 258,172	$ 273,102