Income Taxes - Total income tax provision (Details) - USD ($) $ in Thousands	3 Months Ended									12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Current income tax provision:
Federal										$ 34,124	$ 19,787	$ 18,644
State										16,415	13,178	7,062
Total current income tax provision										50,539	32,965	25,706
Deferred income tax provision (benefit):
Federal										4,645	8,142	8,294
Effect of the Tax Act									$ 5,600	0	(1,441)	5,633
State										2,851	2,574	2,493
Total deferred income tax provision (benefit)										7,496	9,275	16,420
Total income tax provision	$ 13,109	$ 15,492	$ 14,168	$ 15,266	$ 15,376	$ 7,798	$ 10,182	$ 8,884		$ 58,035	$ 42,240	$ 42,126