Stock-Based Compensation Plans (Details 3) $ in Thousands	12 Months Ended
	Dec. 31, 2020 USD ($) period shares	Dec. 31, 2019 USD ($) shares	Dec. 31, 2018 USD ($) shares	Oct. 31, 1996 shares
Additional disclosures
Stock-based compensation expense	$ 21,110	$ 24,885	$ 19,707
Capitalized stock-based compensation cost	$ 9,974	9,396	10,208
Employee Stock Purchase Plan [Abstract]
Shares issued under Employee Stock Purchase Plan | shares	20,161
Stock-based compensation expense	$ 21,110	24,885	19,707
Performance awards
Additional disclosures
Percentage of stock based compensation elected to be received in the form of stock options upon the election of the recipient	25.00%
Award vesting period (in years)	3 years
Maximum Measurement Period (in years)	3 years
Performance awards | Maximum
Additional disclosures
Percentage of stock based compensation elected to be received in the form of stock options upon the election of the recipient	100.00%
Restricted Stock and Restricted Stock Units
Additional disclosures
Unrecognized compensation cost for unvested stock options	$ 25,200
Weighted average period for recognition of unrecognized compensation cost	1 year 9 months 18 days
Non Qualified Employee Stock Purchase Plan
Additional disclosures
Stock-based compensation expense	$ 537	$ 761	$ 436
Employee Stock Purchase Plan [Abstract]
Employee stock purchase plan, shares of common stock reserved for issuance | shares				1,000,000
Employee stock purchase plan, remaining shares of common stock available for issuance | shares	634,274
Employment period of full-time employees for becoming eligible to participate in the plan (in months)	1 month
Number of purchase periods | period	2
Employee stock purchase plan, discounted stock price percentage	85.00%
Shares issued under Employee Stock Purchase Plan | shares	20,161	13,894	12,955
Stock-based compensation expense	$ 537	$ 761	$ 436