Business Combination - Narrative (Details) - USD ($) $ in Thousands		3 Months Ended								12 Months Ended
	Jan. 04, 2019	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, 2019	Dec. 31, 2018	Dec. 31, 2017
Business Acquisition [Line Items]
Intangible assets		$ 60,900								$ 60,900
Goodwill		137,823				$ 0				137,823	$ 0
Net income available to common stockholders		$ 262,856	$ 267,281	$ 317,987	$ 288,732	$ 266,264	$ 274,817	$ 237,798	$ 194,961	1,136,856	$ 973,840	$ 490,506
SVB Leerink
Business Acquisition [Line Items]
Total purchase price	$ 273,230
Retention pool for acquiree employees	$ 60,000
Vesting period of retention pool for acquiree employees	5 years
Post-combination expenses	$ 9,100
Intangible assets	60,900
Goodwill	$ 137,823
Net income available to common stockholders										$ 9,524