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Share-based Compensation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Jun. 30, 2019
Stock Option Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option awards granted	0
Options outstanding, shares	1,326,000		1,326,000		1,459,000
2013 Equity Plan \| Stock Option Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option awards granted	0
Stock options vested	27,500
Aggregate fair value of stock option vested	$ 1.8
Weighted average grant date fair value of stock option awards		$ 50.57
Share-based compensation expense recognized	1.8	$ 3.0	$ 7.8	$ 11.1
Unrecognized share-based compensation expense	$ 21.0		$ 21.0
Unrecognized compensation expense expected to be recognized			2 years 6 months
2013 Equity Plan \| Other Stock-based Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense expected to be recognized			2 years 8 months 12 days
Other stock-based awards granted	0
Unrecognized share-based compensation expense	$ 0.4		$ 0.4
2013 Equity Plan \| Class A \| Stock Option Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option awards granted	0
Options outstanding, shares	1,326,233		1,326,233
2013 Equity Plan \| Class A \| Employees, Officers, and Directors
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation, stock authorized	2,300,000		2,300,000
Shares of class A common stock reserved and available for future issuance	677,500		677,500