Commitments and Contingencies (Details) - USD ($)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Rental expense for operating leases	$ 2,300,000
Defined benefit plan employer matching contribution on first five percent of employee compensation	50.00%
Percentage of employees' eligible compensation for employer matching contribution	5.00%
Defined benefit plan employer contribution limit	$ 6,000
Defined benefit plan employer contribution vesting period	5 years
Defined benefit plan employer contribution	$ 500,000	$ 400,000
Letter of Credit [Member]
Line of Credit Facility [Line Items]
Proceeds from amounts drawn against letters of credit	0
Letter of Credit [Member] | LOC for Office Space [Member]
Line of Credit Facility [Line Items]
Letters of credit outstanding	1,900,000
Letter of Credit [Member] | LOC for Security Deposit [Member]
Line of Credit Facility [Line Items]
Letters of credit outstanding	$ 100,000