Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 82,258	$ 81,597	$ 164,660	$ 155,958
Securities available for sale:
Change in unrealized gain during the period	716	380	1,219	580
Total other comprehensive income	716	380	1,219	580
Deferred taxes related to other comprehensive income	(150)	(80)	(256)	(122)
Other comprehensive income, net of tax	566	300	963	458
Comprehensive income	$ 82,824	$ 81,897	$ 165,623	$ 156,416