Business Combination - Narrative (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
	Jan. 04, 2019	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Business Acquisition [Line Items]
Intangible assets		$ 60,900		$ 60,900
Goodwill		137,823		137,823		$ 0
Increase to goodwill due to measure period adjustments		2,600
Increase in cash paid due to measure period adjustments		2,300
Net income available to common stockholders		317,987	$ 237,798	606,719	$ 432,759
Investments
Business Acquisition [Line Items]
Increase (decrease) in assets acquired due to measure period adjustments		700
Accounts receivable
Business Acquisition [Line Items]
Increase (decrease) in assets acquired due to measure period adjustments		(1,000)
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		$ 3,858		$ 9,703