Summary of Significant Accounting Policies - Commitments and Contingencies (Details)	3 Months Ended		6 Months Ended
	Jun. 30, 2019 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($) ft²	Jun. 30, 2018 USD ($)
Accounting Policies [Abstract]
Operating cash flows for lease liabilities			$ 28,202,000
Square feet of office space | ft²			60,293
Monthly rent payments			$ 99,232
Rent expense			600,000
Lease, Cost [Abstract]
Operating Lease, Cost	$ 16,261,000	$ 15,230,000	31,331,000	$ 29,783,000
Variable lease cost	$ 3,348,000	$ 3,042,000	$ 6,607,000	$ 6,063,000
Weighted-average remaining lease term (years)	4 years 5 months 26 days		4 years 5 months 26 days
Weighted-average discount rate	3.50%		3.50%
Lessee, Operating Lease, Liability, Payment, Due [Abstract]
2019	$ 24,460,000		$ 24,460,000
2020	52,655,000		52,655,000
2021	41,439,000		41,439,000
2022	32,093,000		32,093,000
2023	20,099,000		20,099,000
Thereafter	19,413,000		19,413,000
Total lease payments	190,159,000		190,159,000
Less: interest	15,087,000		15,087,000
Present value of lease liabilities	$ 175,072,000		$ 175,072,000