Statement of Cash Flows - Noncash Investing and Financing Activities - Additional Information (Detail) - USD ($)	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Supplemental Cash Flow Elements [Line Items]
Noncash investing activities incurred for fixed asset acquisitions	$ 15,119,000	$ 12,600,000	$ 10,410,000
Common Stock [Member] \| Stock Award Plan [Member]
Supplemental Cash Flow Elements [Line Items]
Noncash financing activities shares issued	99,497	35,372
Noncash financing activities issued value	$ 7,931,000	$ 2,941,000
Tebras And PBC [Member]
Supplemental Cash Flow Elements [Line Items]
Noncash investing activities unpaid working capital adjustments related to 2016 acquisitions			$ 4,459,000

The amount of payables that an Entity assumes in acquiring a business or in consideration for an asset received in a noncash (or part noncash) acquisition. Noncash is defined as transactions during a period that affect recognized assets or liabilities but that do not result in cash receipts or cash payments in the period. "Part noncash" refers to that portion of the transaction not resulting in cash receipts or cash payments in the period.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=98513485&loc=d3e4313-108586

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=98513485&loc=d3e4332-108586

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=98513485&loc=d3e4304-108586

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration