Fair Value Measurements - Schedule of Fair Value Information for Financial Assets and Liabilities Carried on Balance Sheet (Detail) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Financial Liabilities:
Revolving credit facility	$ 23,750	$ 9,750
Total long-term debt	161,839	163,695
Carrying Value [Member]
Financial Liabilities:
Revolving credit facility	23,750	9,750
Total long-term debt	161,787	163,635
Carrying Value [Member] | 4.25% Convertible Senior Notes [Member]
Financial Liabilities:
Total long-term debt	131,858	134,075
Carrying Value [Member] | 3.90% Promissory Note [Member]
Financial Liabilities:
Total long-term debt	9,777
Carrying Value [Member] | 4% Promissory Note [Member]
Financial Liabilities:
Total long-term debt	6,982	7,237
Carrying Value [Member] | 3.75% Callable Promissory Note
Financial Liabilities:
Total long-term debt	7,671	7,837
Carrying Value [Member] | 4.55% Promissory note [Member]
Financial Liabilities:
Total long-term debt	5,499	5,611
Carrying Value [Member] | 3.95% Promissory Note [Member]
Financial Liabilities:
Total long-term debt		8,875
Estimate of Fair Value Measurement [Member]
Financial Liabilities:
Revolving credit facility	23,750	9,750
Total long-term debt	169,517	177,334
Estimate of Fair Value Measurement [Member] | (Level 2) [Member]
Financial Liabilities:
Revolving credit facility	23,750	9,750
Total long-term debt	137,460	147,375
Estimate of Fair Value Measurement [Member] | (Level 3) [Member]
Financial Liabilities:
Total long-term debt	32,057	29,959
Estimate of Fair Value Measurement [Member] | 4.25% Convertible Senior Notes [Member]
Financial Liabilities:
Total long-term debt	137,460	147,375
Estimate of Fair Value Measurement [Member] | 4.25% Convertible Senior Notes [Member] | (Level 2) [Member]
Financial Liabilities:
Total long-term debt	137,460	147,375
Estimate of Fair Value Measurement [Member] | 3.90% Promissory Note [Member]
Financial Liabilities:
Total long-term debt	10,565
Estimate of Fair Value Measurement [Member] | 3.90% Promissory Note [Member] | (Level 3) [Member]
Financial Liabilities:
Total long-term debt	10,565
Estimate of Fair Value Measurement [Member] | 4% Promissory Note [Member]
Financial Liabilities:
Total long-term debt	7,421	7,409
Estimate of Fair Value Measurement [Member] | 4% Promissory Note [Member] | (Level 3) [Member]
Financial Liabilities:
Total long-term debt	7,421	7,409
Estimate of Fair Value Measurement [Member] | 3.75% Callable Promissory Note
Financial Liabilities:
Total long-term debt	8,100	7,861
Estimate of Fair Value Measurement [Member] | 3.75% Callable Promissory Note | (Level 3) [Member]
Financial Liabilities:
Total long-term debt	8,100	7,861
Estimate of Fair Value Measurement [Member] | 4.55% Promissory note [Member]
Financial Liabilities:
Total long-term debt	5,971	5,802
Estimate of Fair Value Measurement [Member] | 4.55% Promissory note [Member] | (Level 3) [Member]
Financial Liabilities:
Total long-term debt	$ 5,971	5,802
Estimate of Fair Value Measurement [Member] | 3.95% Promissory Note [Member]
Financial Liabilities:
Total long-term debt		8,887
Estimate of Fair Value Measurement [Member] | 3.95% Promissory Note [Member] | (Level 3) [Member]
Financial Liabilities:
Total long-term debt		$ 8,887