Goodwill and Other Intangible Assets - Schedule of Changes in Carrying Amount of Goodwill (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Goodwill [Roll Forward]
Balance at beginning of period	$ 1,036,994	$ 1,036,258	$ 1,036,994	$ 1,036,258
Acquisitions and adjustments	0	736	0	736
Balance at end of period	$ 1,036,994	$ 1,036,994	$ 1,036,994	$ 1,036,994