Commitments and Contingencies - Additional Information (Details) ¥ in Billions		2 Months Ended	3 Months Ended		6 Months Ended
	Jul. 01, 2018 ft² Floor	Mar. 02, 2018 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2018 JPY (¥)	Jun. 24, 2016 USD ($)
Other Commitments [Line Items]
Rental Expense Relating to Operating Leases			$ 10,454,000	$ 10,371,000	$ 20,571,000	$ 19,888,000
Unfunded Commitments for Capital Contributions			3,255,000		$ 3,255,000
Inter-Bank Balance Interest Rate [Member]
Other Commitments [Line Items]
Debt Instrument, Basis Spread on Variable Rate					0.10%
PNC Bank [Member]
Other Commitments [Line Items]
Maximum Borrowing Capacity								$ 30,000,000
Amount Outstanding During Period		$ 30,000,000
BBVA Bancomer [Member]
Other Commitments [Line Items]
Maximum Borrowing Capacity			10,037,000		$ 10,037,000
Subsequent Event [Member]
Other Commitments [Line Items]
Additional Floors | Floor	7
Additional Floors Commencing on Lease Effective Date | Floor	3
Time to Take Possession of Additional Floors	5 years
Square Feet of Office Space | ft²	350,000
Foreign Exchange Forward [Member]
Other Commitments [Line Items]
Derivative Asset, Notional Amount			20,136,000		20,136,000		¥ 2.2
Derivative Asset, Fair Value, Gross Asset			$ 115,000		$ 115,000