Summary of Significant Accounting Policies - Summary of Impact of Adoption of Accounting Standards (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Jan. 01, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017
Current assets:
Prepaid expenses and other current assets	$ 30,918				$ 21,383
Total current assets	250,397				178,114
Property and equipment, net	43,715				52,255
Operating lease right-of-use assets	52,479				0
Total assets	1,072,329				967,933
Current liabilities:
Other current liabilities	21,644				4,861
Total current liabilities	314,392				257,026
Operating lease liabilities	46,022				0
Deemed landlord liability, less current portion	0				24,484
Deferred income tax liability	5,578				439
Other long-term liabilities	14,330				16,560
Total liabilities	380,322				378,230
Shareholders’ equity:
Accumulated deficit	38,296				(41,487)
Total shareholders’ equity	692,007	$ 658,055	$ 621,897		589,703	$ 564,435	$ 543,127	$ 526,473	$ 503,530
Total liabilities and shareholders’ equity	$ 1,072,329				$ 967,933
ASU 2016-02
Current assets:
Prepaid expenses and other current assets				$ 21,013
Total current assets				177,744
Property and equipment, net				37,613
Operating lease right-of-use assets				51,854
Total assets				1,004,775
Current liabilities:
Other current liabilities				10,951
Total current liabilities				263,116
Operating lease liabilities				45,294
Deemed landlord liability, less current portion				0
Deferred income tax liability				3,158
Other long-term liabilities				14,630
Total liabilities				405,919
Shareholders’ equity:
Accumulated deficit				(32,334)
Total shareholders’ equity				598,856
Total liabilities and shareholders’ equity				1,004,775
ASU 2016-02 | Adjustments
Current assets:
Prepaid expenses and other current assets				(370)
Total current assets				(370)
Property and equipment, net				(14,642)
Operating lease right-of-use assets				51,854
Total assets				36,842
Current liabilities:
Other current liabilities				6,090
Total current liabilities				6,090
Operating lease liabilities				45,294
Deemed landlord liability, less current portion				(24,484)
Deferred income tax liability				2,719
Other long-term liabilities				(1,930)
Total liabilities				27,689
Shareholders’ equity:
Accumulated deficit				9,153
Total shareholders’ equity				9,153
Total liabilities and shareholders’ equity				$ 36,842